I can tell you some opposite examples, think of (the 32-33 years old) Kobe Bryant, Tim Duncan, Pau Gasol, Ray Allen, Tony Parker, Vince Carter, Zach Randolph, Paul Pierce, Kevin Garnett. Or even in the past, Jordan, Olajuwon, David Robinson, Stockton, Karl Malone, etc. Yes, there are players who quickly became worse but that's not the average (at least in basketball). Great players are great at mid-30 age too.
AI and T-Mac are different cases, one is simply stupid, the other had injury problems (and I'm sure that if you bring 50 examples, 45 of them will be the same, mainly injuries).
Have a look at LeBron and Melo, they will be 30 this year. Do you think they will lose their skills in 2-3 years?
Don't feed the troll