I wouldn’t call 24 very young in modern football. I would call Mbappe a very young footballer.
In terms of quality if your judging on premiership goals then he meets that criteria. However I think Madrid and their fans would look at other criteria. He hasn’t made a huge impact at champions league or international level, his goals haven’t led spurs to trophies, he doesn’t have that definitive game like Bale against inter.
On top of that he is not a commercial brand, has only ever scored prolific for one team and I assume he doesn’t speak Spanish. I think there are plenty of reasons not to gamble close to a world record fee. I think if you look at things from a Real fan perspective instead of a regular premiership viewer he isn’t a player that has massive appeal. Of course that all changes if he has a great World Cup.
My guess is that Reals main target is Neymar and they won’t spend huge on another forward, unless the World Cup changes everything.