One major sign that you're getting old, developing an adult brain and becoming very very boring is when you gradually stop watching MTV. For me, that transition occurred in the early aughts during my mid-20s.
I was obsessed with MTV during high school and college. It was channel 30 on Cox cable, and TRL, Real World, and even 120 Minutes were all required viewing, but watching the network gradually became more of a chore than a joy. This was before everyone had a TiVo or DVR, and there were only so many Oxy and Revlon commercials a guy could suffer through.