The more elite the cruise the older the crowd. I don't remember seeing many young people on WindStar and Azamara. Not sure how Seabourn, Silversea, Viking etc. compare. The older I get the less tolerant I am of loud partiers and noisy kids. Getting old happens to everyone except the unlucky or foolish.
Though if you watch Bravo's below deck you will see plenty of the young foolish party crowd. Money doesn't buy class.