Age Gaps in dating

So ladies and gentlemen ive heard something that might disturb yall... so im not sure if this was happing back in the days or things changed, so ive heard some elders saying us ma 2000 the people that we date are like ma 2010 and upward (meaning if someone is in his mid 30's his target is ma 2000) so nna id like to know when did this decision happen