While I don't doubt that the 6 series is a great car to drive (the gf's dad had a 640d which was lovely), it has a different image to the 3 series which in my mind more suits the older driver.
I don't think I will ever understand the reason people seem to try and group cars into age bands, do you think driving a 3 series makes everyone think you are young and carefree or something

If I could afford a current shape 6 Series I would buy it tomorrow!