I think both have a role in the decline CR7's performance at Manchester United at this time. the age factor, he still seems to have good enough stamina to play 90 minutes. However, the EPL is quite tough, Ronaldo can lose in a body fight with other players when dribbling / grabbing the ball. As for the duet friends, Ronaldo planned to partner with Cavani at the start of the season, but Cavani is also too old, while other players seem to need time to be able to play with Ronaldo style. Ronaldo partner must also have speed so that they can balance each other in the process of attacking the opponent's defense.