I know that many autistics tend to appear younger than they are, both physically (for some unexplained genetic reason) and socially (because our lack of typical social savvy may make us seem childlike). In my case, my speech issues also play into this. In the past week I've started to notice that this is becoming a problem for me. I'm taking a job training course, and although I can't be more than a few years younger than some of the other students, I'm treated as the class baby. I'm frequently described by such terms as "precious," "adorable," and "sweet." These aren't insults, of course, but they're also not quite the competant, mature, professional image I'm trying to project. I'm trying to train myself to lower the register of my voice to sound less babyish, but in a social setting in which I'm focusing all my energy on being able to talk at all, it's hard to remember.
Also, not to get to personal, but I'm trying to enter the whole dating scene/meet a mate thing, and I think the childlike appearence and voice are impediments in that area. The only men who show any kind of romantic interest in me are pervy old men who I suspect are borderline pedophiles--not quite what I'm looking for.
Is there any kind of solution to this?
You'll appreciate it more when you get older.
But it was admittedly odd when I got carded at a restaurant while doing a job interview. (I was 37!)
Is there any kind of solution to this?
None that I'm aware of, sorry.
I'm told that I look much, much older when I wear makeup, so you could experiment with that. But otherwise, I really have no advice.
I can relate, though. I am fifteen but look twelve; my bf is 16 but looks 20, so you can imagine we get some odd looks.
Oddly, I've found that the following is true:
1. In my appearance, I seem younger than I am.
2. But when people talk to me, they assume I'm older than I am- often they guess about 18.
3. Unless they see me when I'm tired, at which point I act like a bratty five year old. I also act about 7 when I'm really excited.
4. Because of this, people end up viewing me as a spazzy girl who is very immature but wise beyond her years and very talented, which confuses a lot of people.
5. People who meet me online often assume I am in my twenties or older because (particularly if I've just been reading something) my writing can be very "adult" seeming and I never use "chatspeak" or abreviations or the like.
So, yes, I've experienced some of what you describe.
I have heard of voice coaching for people who want to lower, strengthen or otherwise improve their speaking voices. I saw this coaching demonstrated on TV some years ago, with one of the subjects being a grown woman with a little-girl voice, and she did end up sounding much more adult. I don't know if there is any such coaching in your area or what it would cost, but it might be worth looking into.

I'm 57 and I don't get carded any more either. My hair's turning grey, so I really don't look all that young anymore--people typically guess mid to late 40s.
I know what you all mean, though. I had the same problems growing up--seemed like nobody took me seriously when I was trying to prove myself intellectually because not only did I look and seem a lot younger than my age but I also came across as disjointed and scattered--so people thought I was ditzy. If somebody encountered me through writing rather than in person and then later met me, I'd get comments like "you really wrote that?"
Here in Australia they also ask for photo ID to buy things like Box Cutters, Pocket Knives, Fishing Knives, Utility Knives and even Leatherman Tools.
I was getting asked for ID in some cases right into my late 20's unless I wasn't wearing my sunglasses and cap at the time. Yay for male pattern baldness. Most people still tend to assume I'm in my twenties - I'll be 36 this year. I attribute this mostly to the way I dress. I'm not overboard on fashion but I avoid button-down shirts, ties, dress pants and the like as I prefer Jeans and tshirts (the long sleeve kind in winter) sneakers/cross-trainers or hiking/work boots. I have some short-sleeve casual shirts (with buttons) but I tend to only wear them in spring/summer when I'm dressing up a bit. (Dinner at a resturant - or social club with a dress code - or family parties like xmas and new year)
So yeah, in my opinion there's a significant element to how you dress, act, speak and carry your self.
I wouldn't worry about it. Looking young is a benefit.
Also, I wouldn't buy into the idea that every older guy who shows interest in you is a pervert. Some may have the best intentions, and an appreciation for you that men your own age can't even fathom.
I don't mean that every older man who is interested in me, or any younger woman, is a pervert, but these particular men, I believe, are. They are men in their 40s and 50s who tell me how "sweet" and "innocent" I am. It creeps me out.
Maybe "looking younger" isn't quite the best way to describe this phenomenon, because I don't know that I necessarily look chronologically younger than I am; it's more like "looking childlike." I think I look, or give off an aura, like a child in a young adult's body, or something. I don't know if it's my walk, my voice, my face, my body, my clothes, my (lack of) social grace and speaking ability, or what, but there's *something* that's bringing out people's "ooh how precious" instinct.
That's (Yetti's advice) exactly what I would suggest. Or a music teacher, ie; singing.
I look younger than I actually am, mostly due to my inability to grow any facial hair. I'm 21, and I still get carded for R-rated movies, not to mention alcohol.
female aspies have a higher date rape % than any other group.
Where did this statistic come from?
(and yes, it did happen to me, except that's not what they called it back then)
My whole family has also had the problems (when young) and advantages (when old) of looking younger than our age, and perhaps it is a combination of looks undamaged by NT facial expressions (our faces are relaxed most of the time as we aren't constantly worrying about how others see us) and a more youthful outlook (note that I refuse to use 'immature'!).
A few years ago (I was 42) I was asked for ID when out with my son and his college friends - we were ALL old enough to buy alcohol, but it was amusing to be thought one of them!
My husband is also thought of as much younger - in fact, only last month someone thought that we were 'pushing forty' and was shocked to hear that I'm nearly 50 and he's 52!
I look 15ish at 20. If you judge by face only, maybe even younger (about 12) but I'm too tall for a 12-year-old hehe

Up until I was about 24, I still got people asking me "Is your mommy or daddy home?" when I opened the door. And one of my psychiatrist's reports describes me as "childlike" for some reason I don't understand. But it seems to run in my family, not sure it has to do with autism in my case. My mom looks young for her age, and so does her mom.
I like lookng young for my age.
I am 'backwards' for my age, and while I look 'young' it can 'get away with' this.
I worry what happens when I don't look young anymore because then it will be obvious to people that I am just backwards and I have learning difficulties, and they won't respect me and will say I'm ***.
Regarding speech coaching, I saw an excellent drama teacher who also helps people with speech impediments. She helped me to have more tonal variation in my voice and to learn some basic body language. She aslo helps people with public speaking and with making their tone and pitch of voice appropriate to the situation, as this is something actors have to do all the time.