2nd he is basicly a easter egg character that doesnt follow continuity
I think that's the answer, really. Being an easter egg, M'aiq doesn't need to make sense, while he hasn't managed to live beyond the natural lifespan of his race as of Oblivion, to our knowledge, his dialog borders on breaking the fourth wall, so it seems obvious that he isn't meant to be taken seriously as an actual part of the world, so if Bethesda decides they want him in Skyrim, he can be in Skyrim, no matter when it's set, this doesn't mean he will be in the game, of course, it just means it's not impossible for it to happen.
Aw I hadn't thought about it that way. However some races have a better life span like an Elf could still be alive in 200 years from the last game. Don't suppose khajits have that sort of shelf life though.
I doubt that, it's been said that elves have longer lifespans for humans, however, for those races whose average lifespans have not been specified, we can probably assume they're similar in length to what we would see in real life humans living under similar conditions to those in the Elder Scrolls. So, we can safely assume, it would not be natural for a Khajiit who was alive at the time of Morrowind and Oblivion to be alive now.