I've played guitar since I was in 3rd grade, with a few skipped years and I'm 33 now. I can't "shred" at all though, never was interested in playing guitar that way but I do some enjoy some bands or just people who do. I bought a 5 string bass guitar in 2012 but I only got it because I write and record music, so having a bass in there really helps fill out the sound, so I can play bass but not like any real bass players like John Myung from Dream Theater.
I don't really practice either instrument at all, I just pick them up and noodle around with them, if I come up with a riff that I like but can't play well I just practice that rather than more traditional practicing. Years ago I would learn how to play mildly difficult songs which improved my playing a bunch, I mainly listen to metal so I learned some songs from bands like Metallica, Meshuggah, Opeth and stuff like that.