Fellaini left United in January for Shandong Luneng.
The Ole Gunnar Solskjaer regime seems committed to regenerating their squad with a younger profile of player.
But Fellaini told the Daily Mail: "Now you have a new manager, they wanted young players and that's what happens when you play with just young players - they will be up and down, up and down, that's football.
"Of course in football, you can't play with just young players, you need a mix. I think to win games, to win titles, to win big games you need experience. Of course you can win with young players but not every game."