I've only had Tamas for just over one year - but there are plenty of members on this site who have owned a Tamagotchi for years! (before the V1 and V2 were launched)
I have had my tamagotchi for some time.... its on 12 generation never died... except its battery ran out and I couldnt find the right battery for a LONG time so I would be at 20 generation now....