A 38 year-old athlete performing at the same level as they did in their mid-20s (or in this case, slightly faster) is highly unusual. Look at all the suspicion Bernard Lagat generates, and he was not as fast at 38 as he was in his prime. In his best event as far as his whole career goes, the 1500 (the more speed-oriented event), he was significantly slower.
Look at the suspicion generated by Regina Jacobs when she set an indoor WR at age 39. (This suspicion proved to be well-founded.)
Look at Eddy Hellebuyck when he turned 40.
Or, by contrast, look at Gebrselassie. He continued to run some good races at age 38, and everybody talked about what an ageless wonder he was. But those races were not close to career bests. Can you imagine him running under 26:22 for 10k at age 38? Would people find that believable?
What if Paula Radcliffe broke her marathon WR as a 38 year-old? Would that not be suspicious?
People don't age slower than they did a generation ago. Some people take better care of themselves perhaps. But most of the time when an athlete is still performing well in their late 30s, if you take a sport like baseball, it's a superstar who had so much skill to begin with that they are still good even in a diminished state. They are not actually as good, or better, than they were a decade earlier. They don't get faster as they age.
Can anyone name a single sprinter who has been faster at 38 than at, let's say, 27?
I don't say Kim Collins should be considered guilty of using PEDs merely because of his late-career surge (or ability to maintain, if you don't want to concede that he's faster). I just say, look, this is unprecedented and extremely surprising (and we know what that often means in modern sports). Don't act like it's something that happens all the time nowadays, when in fact it has happened a grand total of one time.