The Welsh midfielder hits the age milestone on Friday and is of the belief that if he had ever left Old Trafford, he may be finished by now.
"If I'd moved from club to club I'd be finished by now," said Giggs. "I'm lucky that I have been at one club, where I am surrounded by good players. I also have a good manager.
"I look after myself and try to train every day in order to make myself available for selection.
"I enjoy it as much as I can and, of course, try to contribute to the team."
Of his aging years, Giggs added: "I don't know what the younger lads think of me. When I was 17 and 18 I thought 31 was ancient. Here I am at 40.
"It can be hard sometimes but I am still enjoying it.
"As long as that is the case I will carry on."
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