Based on one well known vintage Tamagotchi owner's logs (Kat of Mimitchi.com), I'd say the best care character - Mametchi in this case - will live up to 21 days. However, the secret characters Oyajitchi/Bill will live up to around (I think) 31 days, possibly by virtue of evolving from an adult character. The vintage Tamagotchis are programmed to die at a certain age, unlike the later models, but this can be altered somewhat by changing the clock. I say somewhat because the tamagotchi will have the same programmed time to live but when that happens in real time will be different. For example, if the a P1 is set to die at 6:30 and the clock is moved ahead one hour, it will die at 7:30 instead. Similarly, if a P2 is set to die in 18 days and the amount of time its clock is forwarded amounts to 2 days, it will die in 20 days. Additionally, when a vintage tamagotchi wakes up it will be one day older even if it technically hasn't been active for a full 24 hours.
