You would be at the younger end on a JY holiday, the main age range is 50's & 60's.
Saying that there are others either side of that on the 4 trips I've done so far the youngest as been in their 20's on 2 trips and mid 30's on the other two.
I must say I havent seen age been a issue on any of the trips everyone seems to get on great. If you are worried I suggest before you book you use the "ask the editor" section of this forum to ask age range of those booked on any specifc holiday.