Villas-Boas only has two seasons of top-flight experience in the Portuguese Liga behind him - his performance at Porto last season was impressive considering he won three trophies, including the Europa League, and the title.
And at just 33, he is the same age as some of the players he has taken charge of at Stamford Bridge.
"It is a big step for Chelsea and an enormous challenge," Ferguson said.
It took the Scot back to the start of his own career almost four decades previously.
"I was 32 when I started but I was managing a wee Second Division team in Scotland," Ferguson said.
"All I had was a physio. I had no assistant manager or anything like that.
"He has the advantage, irrespective of his age, of having the staff he wants to have.
"It is a strong possibility he will have enough staff to overcome that type of move."
"He knows the club," added Ferguson.
"He has been there before so that is an advantage.
"He has a very experienced bunch of players there and for a young manager having to go to a club of that size, experienced players are a help to him.
"We expect Chelsea to be challenging again."