Barcelona can't do that. This can be done by Ajax or Sevilla or Borussia. Top European clubs have to sign best players and not only young players since they have to continue wining all of the time. You can incorporate 2 or 3 very young players like we are doing now with Dembele and probably Alena next year but you can't do that with 50% of players. Also Umtiti, Mats, Mina, Semedo, Coutinho and Sergi Roberto are still young. Alba is also in his best years, so I would say we are not an old team, not even near that. When you are talking about Griezmann you are talking like he is an old player while he is 26 years old. He for sure has 4 or 5 years left on top level in his feet, for me that's more than enough.
What we will need the most is one young controlling CM player but I believe we are working on that also.
Can't do what? We are already signing stars, it isn't like I am saying we should just sign prospects and players from France. You are making it like Barcelona should build a team of Galacticos and only sign expensive players, that is what we can't do
And what 50% of players? We only have Dembele who is going to be younger than 24 next season from current squad, and you can't just say "very young players" on him, he was signed as young super star, was one of best players in Bundesliga and one of most expensive in history and we will need to incorporate him in our attack along Coutinho himself, may be if one of them proved that he will never add something to our attack we can worry that much about adding Griezmann
All the players you are mentioning are the middle of their twenties, they are already in their prime or near there prime , and for the record I gave examples, we could go for older or younger players, forget the names
And he will be over 27 when he is signed for the record, he won't be old but I would prefer someone who isn't from same exact generation of half of the squad, or little older
Griezmann is neither an urgent need, or sure thing to fit in the team or a can't miss opportunity, neither is he going to come with fair price unless he is stupid and ask less than he can get, I would honestly prefer to be patient and see if there is someone else evolve in the market next season rather than blow the whole buget on him
Here is a list of most expensive players in history, only 2 players from top 15 was 27 or older (VVD is a bit close to that age too tbf)
https://en.wikipedia.org/wiki/List_of_most_expensive_association_football_transfers
8 out of 38 players in the list transferred after 2009 was 27 or older, many of them are questionable deals
There is a surely trend about younger player being the more expensive ones tbh. Less than decade ago it was normal that a 29 years old player to be very expensive but that isn't really the case anymore tbh