Surely this doesn't need explaining, if you've bothered to read my comments? Nolito doesn't mind sitting on the bench, so they can play when it suits them, or we can use Nolito's experience. Sanchez will demand to play every game, like Aguero, and like Sanchez already does at Arsenal. So you can't play the kids at all because Sanchez and Aguero both have to start, leaving 3 kids fighting for 1 place each week.
Guardiola doesn't believe that and has never said it. If he did believe it he wouldn't have binned Henry for 20 year old Pedro, or Yaya for Busquets.
We don't have to wait 5 years for them to come of age either, that's just bullshit and everyone knows it. In two years, Sané will be 23 and Sterling 24, and they'll want to be at a club where they play every week. Meanwhile Sanchez will be 31 and still expect to start every week.
We made a deliberate choice to buy the next generation of world class players. England, Germany and Brazil's biggest attacking talents all joined in the summer, and we spent big to get them before the likes of Bayern/Barcelona/Real did and they became unavailable.
So if we've already made that decision to get the next generation, deciding we actually need a 29 year old for another £50+m and then losing the next generation because we played Sanchez into his 30's would be a massive failure in the transfer market.
If we had to have someone of Sanchez's level now, or next season, we should never have been spending £130m on the kids.