At the same age Lewandowski was playing for Lech Poznań and Allardyce was looking to sign him for Blackburn, Cavani was playing for Palermo, Suarez was playing for Ajax, Firmino was playing in midfield for Hoffenheim, Lukaku had been binned off by Chelsea and was on loan at West Brom, Ibrahimovic was at Ajax... none scoring that many more or less than Gabriel Jesus is for City.
Apart from Gonzalo Higuain (Real Madrid, starter at 20) and Wayne Rooney (United started at 19) no other striker (proper #9) at 21 year’s old was at a proper top club, Benzema and Agüero were two others who were banging the goals in but at Lyon and Atléti. and most of the ones who are top players now had not even really been heard of yet.
Gabriel Jesus might stay at the quality he is now, never really making it at the top level like Balotelli never did... but he might also improve between the age of 22-24 and end up being one of the best in the world.
At his age in his position, it’s very hard to tell.