A big thing for me that causes an RP to die off is the lack of plotting and OOC chatting. That seems to be the cause of a lot of rps dying off, they just never seem to get anywhere and I can't get excited about it. Now those are the ones that kind of die off earlier.
For ones that die off...
I don't one I ever too old to RP, I mean I know people who are doing it in their 30s and they use it as a way to creatively write with someone else which makes it a lot more fun. Some people use it as a hobby and others as a way to escape or relax. One of my friends and I have multiple AUs set...