I don't always feature in my dreams- sometimes it's just like watching TV or being in someone else's body- but when I do dream as myself I am my own age.
Excellent question. However, a full answer requires that a respondent give their ACTUAL age. There's nothing very odd in a 16 year old dreaming they are 16. A 70 year old who regularly sees themselves as 20 is much more interesting.
For the record, I am 50 but in my dreams I'm always younger. It's difficult to say but I'd guess it ranges from 25 to 35.
Without wishing to be spooky, I think that people I dream about - for example, my grandmother who is now many years deceased also appear younger. In my dreams she is about 55, the age she was when I was only 2 or 3. So in one dream I can be 30, my grandmother 55 and my late father perhaps 35! I guess that's the joy of dreams.