I don't think you should nor can you buy young players exclusively (for arguments sake, players under 25). On occasion you do need to supplement the squad with some experienced heads, who are still performing at an elite level.
In this particular case, I think a player of the stature and character of Vinnie leaving does leave the risk of a leadership vacuum, both on and off the field. I would be against spruiking huge money for a player 28 and above, but in the case of Alderweireld for example (I don't want Bonucci for tbf for various reasons), it would make so much sense. We'd also then be able to bring along a young talent like Garcia according to plan, so that he's ready to go when Otamendi leaves.