I hope he can retire with Manchester United, I know Ronaldo is not a money-hungry person because everyone knows the wealth he has made from football, but he is hungry for titles and wants to write a sweet story at the end of his career.
Ronaldo has indeed entered the era of the end of his career, his age has made his performance decline but it doesn't look like he will retire anytime soon, I think his desire to get the world cup trophy for his country is the reason for him to continue playing at this time, for club level Of course it looks like he will not retire at Manchester United because he previously said that he would end his career at his childhood club, Sporting Lisbon.
I can't Really tell when Ronaldo will retire but it seems anytime soon. I'm sure Ronaldo won't play Champions league again till he retires, that's is why he was looking for a way to leave Manchester United because he knew this Champions league is just the last chance for him and never wanted to miss it . Age is really affecting Ronaldo's right now, because he is not too much active the way he used to be. If I can remember Ronaldo have only scored 1 goal for Manchester United in Europa League this season.