Five owners on a 12 year old m3. That's a lot...
No it isn't. Not on a car like that. Cars like that are toys, playthings. Certainly in their early lives. I would keep a car like that for 12-18 months, then move onto the next one.
That car has had average ownership length of 2.4 years. That's pretty decent going for a car like this. If it had 12 owners, I might be a little more worried. But 5? That could almost be classed as a low number of owners, for that car, at that age.