The mc's still aging unless he dies, at which point it's like he's teleporting (it's not like he's deaging when he goes back in the past as seen when he went back 11 years), right? So if that's true his body can still get older but he would never die because he can just go back in time. Might be annoying when he's an old man, but at least he can visit the past for some nostalgia (even if he does have to live in that time since he can't go to the future)