The average age of the old players shouldn't be a problem if the players are still able to do hard training, so that when the performance on the field is good and reliable, experience will be an important key for the old players. So it's better to save money to buy players who really need it than just for rejuvenation.
As long as the age of players are not too old and it must not be a problem. The problem is if chelsea doens't have good chemistry as a team. Some players were even playing individually. Medueke was very often doing it by dribbling the ball for their own.
Mudryk is always having horrible finishing. He shall have learned how to create a proper finishing. He is always feeling panic when he will be 1 on 1 against the goal keeper.
Sterling is always missing so many golden opportunities. Almost all of chelsea players have horrible finishing. They can't properly finishing the chance into the goals.
That being said that those people shall have learned a lot about how to create a proper finishing.