I did Peru last September and it was fab.
I've done about 10 JY holidays and they have all been great.
Age ranges have been anywhere from 30's to 70's (I'm 42) but age ranges don't matter everyone mixes and enjoys the company
Women do tend to outnumber the men.
Group sizes varies small one I've been on is 13 and largest 40
Book holiday that appeals to you and you will enjoy
Anna