Sebastian Vettel may be past his prime in formula one.

That is the sensational claim of F1 legend Sir Jackie Stewart, after the Ferrari driver lost the 2018 title to Mercedes' Lewis Hamilton.

"I think Sebastian is past his peak and Lewis is still building to his," the triple world champion told Bild newspaper.

"There's no reason Sebastian can't come back, but it will be very difficult because after a season like that you are more critical of yourself, and what you want to do and what you don't want to do," Stewart added.

At 31, Vettel is actually two years younger than Hamilton, but Stewart thinks the problem could be that the German won his four titles too soon.

"Perhaps. He came into formula one at 20 and was a four time champion by 26," said the Scot.

But the biggest reason is that Vettel has simply made mistakes in 2018, Stewart added.

"It's not possible to keep blaming everyone else. If you fight for a world championship and you see that a move you make could be a problem for you, you don't necessary try it. You wait for the right moment," he said.

"I like Sebastian very much and he is a very good driver. Very emotional, and technically maybe still the best, but he does not have that clear mind like he used to."

In contrast is Hamilton, who Stewart says can now be "even more relaxed" in 2019 with five titles in the bank.

And now in his sights could be Michael Schumacher's seven titles and 91 wins.

"Yes he can, and for many reasons," Stewart said of Hamilton's last remaining goals.

"There are more races these days, the management is better, the factories are better, the teams are bigger, and there's more money to succeed than ever before."