As most folks know, the animation business — even the part that programs for adult audiences — likes shows featuring young characters. There have been studio and network execs who have explicitly spread the word that they aren't interested in any show where the major characters are over 16 years old.
So it's interesting that as this article points out there are currently cartoon shows in production where the lead characters are Carl Reiner (age 81), Robert Evans (age 73) and Hugh Hefner (age 77).
I don't think there's any "new trend" here. It's just nice to be able to point out the exceptions.