The 20-year-old joined United from Spanish giants Atletico Madrid in a £18million deal earlier in the summer.
Fergie insisted: “I went to see Petr Cech when he was at Rennes. I said to myself, ‘Yeah, he’s too young’.
“But Chelsea bought him at the end of the season for £7m and he’s never been out of the team.
“So age doesn’t matter when you have the ability of a goalkeeper like Petr Cech or, we know, David De Gea.”
Ferguson added: “David is young, he’s quick, he has fantastic presence and composure and his use of the ball is outstanding.”
