Ok, take the Brazilian league out of the equation. Neymar joined Barca at 21. Between the age of 21 and 25 Neymar has more goals than Ronaldo.
Arguably better than him at 25. Ronaldo now is miles ahead though. It's not impossible that Neymar could reach that level though.
Then again he might go to PSG and flop, that's the thing about potential. You never know how it'll work out.