Tama-go Old Man age 5

My sisters Tama-go hatched the same day as mine and at age 5 hers evolved again into the old man. Why so soon? SHe didnt take very good care of it is that why maybe?

that tamagotchi was probably an adult, if it was a boy, it could be the son of two old timers, resulting in a male old timer baby, for more information on this, check out my tama-go growth chart here.

kuchikid, hebb said that their sister's Tama-Go hatched at the same time as theirs, so she wouldn't already have mated oldies and received Oyajitchi.

This has been discussed over on Tama-Zone (link). It seems that different characters have different aging times - some have claimed their characters to age around age 6 like your sister, and have claimed to age around ages 9, 15 there has even been an age 30 Kikitchi who never reached oldie stage.

I myself have been wondering if it has anything to do with care - better care characters live longer lives, and bad care characters live shorter lives, hence transforming into Oldie stage faster than other characters. I guess this will have to be tested more to be proven accurate, however.