Agree to most part but in general it seems the trend now is to get players when they are younger between 20yrs-24yrs. (This is especially true for Madrid, probably learnt it with the Hazard transfer although they have been doing this for some time now)
Aside from football related reasons, I think it makes sense in terms of finances. As well as likely paying a smaller fee and wages for players at 20 - 22, you have a higher likelihood of recouping some of your investment upon a resale, or even making a profit after years of service.