Sergio Jr. already won his first pro show, and a pretty good pro show at that. The Night of Champions was a top three bodybuilding contest - in 2001 for example, only the Arnold and, of course, the Mr. Olympia were bigger. Even today, this remains the case.
I see no reason why Sergio can't be top 10 in the Arnold and top 15 in the Mr. Olympia already. So if we can say he is currently the 15th best in the world right now, I see no reason why he can't be Mr. Olympia by the time he is 35-40.
Sergio Jr. stated in the Generation Iron interview that Sergio Sr. lied about his age on his birth certificate when he defected to the USA. So he was born around 1935, making him 50 when he came into the1985 Mr. Olympia looking amazing.
That means that Sergio Jr. can probably be competitive for another 20 years.
Do not write Sergio Jr. off just yet...I believe his mother, from Dave Palumbo's recent New York Pro win interview with Sergio Jr. when she said that he will go all the way to the top. Wait and see. Yes, his Caucasian genetics have given him a bit of a larger waist than his old man, but he still looks extremely good.