It's hard with all young players to make that decision, but especially defenders.
If you look at the players 21 or younger on the clubs books at the moment, in or around the first team squad or on loan. Virgina, Kenny, Holgate, Feeney, Robinson, Connolly, Davies, Baningime, Dowell, Onyekuru, Lookman, Vlasic, DCL, Richarlison. Most of these players are not yet ready to be regular starters at a premier league club, but I would wager nearly all of them will be playing in the premier league, or an overseas league of a similar standard, by the time they are 25/26. I'd also be surprised if more than 3 or 4 will still be with us at that age. The rest will have moved on, either because they weren't good enough for us or they wanted regular football which they weren't getting as part of our squad.
In 3 years time
Virginia , Henry , Lookman , Vlasic and Ricarlison ( if he isn’t sold for mega bucks ) are the only ones I can see with a future here
Maybe Beni but we haven’t seen enough of him and Gana has 4/5 years left in him