No, that's not true.
Age has no impact in game-play or performance.
Where is the effect of low age ?
When the new season starts, I check my opponents in CL and and Cup to see the age of their players (also observing some other things) so to know what I can expect from them later.
A young team probably will increase a lot it's quality in a few days or in the finals.
Also behind a young team, usually there is an active and ambitious manager.