Ronaldo faces his former team for the first time on Wednesday since leaving United for Real.
“I won everything at Manchester United,” he told The Sun. “It was a fantastic part of my life.
“And maybe it was the time I enjoyed my football 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.
“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 anymore.”