It is interesting to see the arc of different top running careers. Centro could still pop some great races, but it would be a surprise to see him on the team for Paris. He did earn multiple medals over a six season stretch. Pretty amazing guy! Talent and racing smarts.
It is interesting to see a guy like Kipchoge run so well for so long (he ran 2:02 last September, but will he even get to Paris?) -- and in fact Bekele is a bit older than Kipchoge and just ran 2:04 last fall. Then there is Lagat, who threatened for a medal in the 5000 in Rio over at over 40 years.
How to explain why some can stay at the top as they get older, and some can't?
Going way back, Ron Clarke didn't even hit world class until he quit running, then came back in his late 20s and started setting world records. On the other hand we have Jim Ryun, who peaked at age 19-20. He still ran a couple great races at 25 (Oly trials close in 51-point, and a fast mile in Toronto after that), but he never regained that early greatness.
The keys, don't get injured, train smart, above all stay motivated/hungry.