Age is an issue because getting old makes you more fatigued, need more recovery time and be more prone to injuries.
Going from 23 to 24 doesn't make you less fatigued or need less recovery time or be more injury resistant.
The two don't balance out, because it's not about quality, it's about the physical load of playing 50 games a season in a very high intensity team. Sané, Sterling, Jesus, Stones, Laporte and Ederson can all become twice the players they were, but if Fernandinho gets injured or can't play 3x a week at the same level, we're still fucked.
So it's really not weird at all.