The Blancos star has reiterated his deep affection for his former club as he prepares to face the Red Devils in the Champions League knockout stages
The Portuguese faces his old club on Wednesday in the Champions League, and has nothing but fond memories of his six-year spell at Old Trafford.
"Yes, Manchester was a very good cycle for me," the 28-year-old said in an interview with The Sun.
"I won everything there. It was a fantastic part of my life. And maybe it was the time I enjoyed my football the most because I was so young.
"To be at Manchester United - one of the biggest clubs in the world - at just 18 was a dream!
"And to play alongside those players you had only seen before on television — maybe that’s why I feel I enjoyed it there the most.
"I’m not saying I don’t enjoy it here in Madrid — I do. But I’m older now, more mature. I’m not a dreamer any more like I was when I was young. I’m 28 now so I’m not at the beginning any more. I’m middle-aged!"
Ronaldo, who tasted Champions League success with the Reds in 2008, has stressed that winning the competition again is his main ambition and is confident he can achieve that with Jose Mourinho's team.
"The Champions League is very special at Madrid because we want to win a 10th European title," the 2008 Ballon d'Or winner continued.
"For me, it is the pinnacle. There are so many memorable matches that remain in the minds of the players and the fans. And I want to make my contribution, I want to leave my mark."