I was with a rag today who was talking about how good he was, and he said you can't expect such a young player to be scoring shitloads of goals, except Haaland, who's an exception.
I agreed, except Owen, Rooney, Shearer, Fowler, Cole, Aguero, Kane, Anelka, Suarez. To be fair, Henry took until he was 22.
Some players become world class later in their career (Drogba, for example), but most properly world class strikers are usually scoring lots of goals from an early age.
The key with any young player is can they get past the stage where everyone sees them as a goal threat and gives them extra attention. We've already seen this a little bit with Doku, with loads of teams doubling and even tripling up on him since his great start to the season.