Yeah all the powerpoints in the world wouldn't have me buying GTAV for a 13y/o no matter how mature he might seem. I got away with buying/playing/watching/listening a ton of games/movies/music I shouldn't of when I was a kid but that was mainly because my parents were just ignorant and I hid the bad stuff. If they were more informed and denied me at the time I wouldn't blame them one bit.
Kids always want to do what the older kids are doing. That will always be the case till the end of time. Saying that, not my kid, so the parents are free to raise him however they wish.
I'm not sure it's necessarily a bad thing though, at least in results.
Basically all my friends and I took advantage of our parents ignorance (all our parents were 1970s/early 80s generation and thus at most had played blocky atari games) to play games like GTA3, Manhunt, God of War, etc, well before our 17th Birthdays.
I can't think of any of my friends from middle school and high school who turned out bad, we are all decent people I'd say lol.
I admit my deep knowledge of gaming will probably mean my kids don't play M rated games (aside from stupid M ratings like Halo used to be), but I'm not sure if that is a bit too overprotective.
There is something to be said I guess for graphical capabilities. GTA3 was tremendously violent, but it still looks cartoony in a goofy way, while GTA5 looks damn real. Maybe that matters.
Although fucking Manhunt still makes me feel yucky inside despite the brilliant gameplay