I'm limited by conscience and finances to two at a time. Since 2002, I've had 8 - but one of them got stolen, I took another back after a week (faulty), sold two of the others for parenting reasons, and sold yet another coz it was buggering up my thumbs and shoulder.
As a kid... Hmm, I had a BMX that I loved until I crashed it and ripped my mouth. I had an old Peugeot racer as a teen which I sold to a mate. I didn't really get into cycling until adulthood.
Good question!
Stu