Sir Alex Ferguson says he hopes to have three more years in charge of Manchester United providing he remains healthy.
Ferguson, who turned 70 on 31 December, began his managerial career in 1974.
: "I hope I have a long time left. I am still enjoying it. We have defeats but compared to what we have achieved, they are minuscule.
"As long as my health stays up, I would hope to have another three years at the club."
Ferguson almost retired in 2002 but later changed his mind and went on to win the Champions League for a second time with Manchester United in 2008.
In his programme notes ahead of the Premier League game against Blackburn Rovers, Ferguson wrote: "This time it is a milestone birthday and I suppose inevitably, Manchester United supporters are going to ask if a man of 70 is up to managing this great club.
"As someone who loves his job I am not about to let my years alone dictate my future.
"At my age health becomes the key issue for a man's work and I am happy to say I have been blessed with stamina and energy that sees me coping with what I admit is a very demanding job."
Ferguson's reign at Old Trafford
- 1,421 games
- 843 wins
- 328 draws
- 250 defeats
Aberdeen manager Craig Brown, the only football boss in Britain older than Ferguson, says the United manager is "too old to retire".
Brown told BBC Sport: "If he had retired 10 years ago, he could have got right into his horses or his golf but now it will be hard.
"He is so into Manchester United that nothing could replace that. Maybe 10 years ago something could have but I'm sure it couldn't now. The longer he's there, the harder it will be for him to leave."
celebrated 25 years in charge of Manchester United in November
, but he had enjoyed plenty of success in Scotland prior to his arrival at Old Trafford.
He had spells at East Stirlingshire and St Mirren before he led Aberdeen to the Scottish championship title in 1980 and the European Cup Winners' Cup in 1983.
"I know him very well, he is a pal of mine," Brown said.
Former Manchester United midfielder
“The thing is, you can't imagine life at United without him. One day it will happen, we are all aware of that, and when it does it will be a great shame because of what he has achieved”
"We played together in the Scottish youth international team and the schools' team, and I know him so well that I just can't see him retiring."
With a laugh, Brown added: "Cathy [Ferguson's wife] won't want to be bothered with him around the house. She is very much the boss there by the way."
Ferguson has won 12 Premier League titles, two European Cups and five FA Cups during his time in charge at Old Trafford.
But Brian McClair, signed by Ferguson from Celtic in 1987 and now director of the youth academy at Old Trafford, believes the Scot's passion for the game is stronger than ever.
McClair, 48, said: "When you are involved in football, the funny thing is that you only think week to week and game to game. Certainly the longest I've ever thought about it was season to season. It never came into my consideration that Sir Alex would be in charge for such a period of time. He's a remarkable person.
"There's not been much change to him. He's still first in in the morning, he's still excited and passionate and he loves what he is doing."