Relax, I'm just arguing my opinion. No need to get offended. If you want to argue that Mbappe was the best 17/18 year old since R9, you might have a point - at least regarding end product since Messi was also unplayable at 18. Mbappe also proved it at a WC, although I don't think he was anywhere near player of the tournament levels of good. Anyway, being better doesn't mean being more talented or having a higher ceiling. That's my whole point. Lukaku was better at 18 than Lewandowski or Kane were, doesn't mean he was more talented or had a higher ceiling. Haaland is a similar case, even more so than Mbappe if you ask me.
The question should always be "how can they improve further?" And if the answer to this is "he has to become more composed and improve his decision making" then it's something that the player can still accomplish aged 25. But if the answer goes "he already is very composed and has great decision making, but he needs to work on his technique" then it gets difficult because these things are developed during the childhood and teen years primarily.