Carlos has already dealt with quite a few injuries...so I believe physically with his style of play he might be done by his early 30s which would be a shame but in line with what we've historically seen from players before the Big 3.
I agree, I don't think his game will age so well all the explosive movements and hard hitting takes its toll especially when you're comepting for everything year in and year out and like you said he's already struggled with injuries at this age.
With Sinner I think when some of these young dudes beocme more of a challenge and make him play longer sets especially best of five with the way he hits the ball it could also be a case of breaking down by around late 20's and early 30's
Their other true rival of those two may not even be on the scene yet.