If we take only marketing goals, then it does not matter how Ronaldo plays. He remains one of the most popular athletes worldwide. Chelsea will buy him for free, which may not be such a stupid decision even if Ronaldo keeps his huge salary. And I don't think that Ronaldo is already that bad (more precisely, he became bad in just a year) - last year he was the top 3 scorer in the Premier League and this year he is retired? Hard to believe.
When it comes to age, you can't do anything when age is no longer by your side, particularly in football game which involves strength, agility, Mental energy, and lot more to play. Looking at his performance in this world, it's clearly seen that he has nothing much to offer in the field Play, and I don't really think that he suits the kind of striker that Chelsea needs right now.
However, buying him is still not that bad since he's on free transfer and there are other strikers already in Chelsea.
On second thought, I think we should consider poor form of Ronaldo as a lack of cooperation with his teammates, not just his age because, in my opinion, Ronaldo's age didn't affect his ability to score goals neither did his age affect his strength and pace on the pitch but I think he's been through a lot lately being a human that has affected his ability to do things they way he ought to do when on the field of play.
Can Ronaldo do well as a Chelsea striker? Yes, he can because he will be welcomed by the fans and the management and the players of Chelsea will love to work with him because just like Manchester City players who will rather not score goals to ensure that Haaland scores a goal in every match Ronaldo will not be under much pressure to get the ball always before he can score goals because his teammates at Chelsea will be doing much of assistance for him to easily score goals.