Everyone's primes are the same. Everyone accumulates the same injuries. Everyone trains the same. Max and Jose both got in motorcycle accidents. Max and Jose both kept sparring.
However, to delve further into it, most fighters begin to experience an athletic, reactionary and ability to absorb damage decline about ten to twelve years in. GSP is considered one of the greats and his career was winding down in '13 after almost twelve years of fighting, prompting him to retire. Condit's descent began in '14 after starting in '02 when he got injured against Woodley. Aldo was a few months shy of his twelfth year in MMA at 29 when he began to lose. Fedor started taking losses almost eleven years in. Edgar wasn't the same thirteen years in. Big Nog eleven years. Liddell hit the wall around that time.
Yes, there are outliers like Mighty Mouse, Jon Jones (wink, wink) Anderson Silva (wink, wink), and apparently Max (who stopped sparring to spare his health and try to stave off decline), but for the most part, the majority of top fighters experience it after or around this time frame and begin to taste defeat more often as reflexes change; wear takes it toll; chins fade; injuries linger; weight cuts get harder; there's more tape available on you.
To hammer home my point: Volkanovski lost to Ilia three months shy of his twelfth year as a mixed martial artist. He's still a great fighter, but at 35, and this far into his career, he'll likely never be the same.