The British actor made the announcement Saturday on BBC Radio 4’s Today, where he said it was official ... saying he felt it was truly time to retire, seeing how he's in a later stage of life and doesn't feel like he has much to offer any more in terms of characters.

Here's how he put it ... "I kept saying I’m gonna retire. Well, I am now because I figured, I’ve had a picture where I’ve played the lead, and it’s got incredible reviews." MC is referring to "The Great Escaper," which came out earlier this year and was fairly well-received.

Mike continues ... "The only parts I’m likely to get now are old men, 90-year-old men -- well, maybe 85, you know? And I thought, 'Well, I might as well leave with all this. I’ve got wonderful reviews. What am I gonna do to beat this?'"

Caine had previously revealed that working on 'TGE' was somewhat difficult for him physically -- which makes sense considering the guy is 10 years shy of 100 years old at the moment.

While he might be stepping away from performing in front of the camera, he's still gonna be getting his creativity on with continued writing -- including a novel he's working on now ... which will be released in December.

Still, it's sad news for fans of his ... and there are many. Michael has had some legendary roles over the years -- including his many collaborations with director Christopher Nolan, notably in the 'Batman' films as Alfred the butler. Of course, there are countless others.