They don't live till 99, i mean maybe it's possible but the longest i have ever had was a Futango-Tenshi(Angel Twins) at age 38, but have heard of someone on a respectable site saying they got it to 78!!!, also Kat at Mimithci.com got a Metal Greymon to 68 on a digimon v-pet!
And yes sadly with the new feature that they turn into an old man/woman for the remainder of it's time on earth
(before it goes back to the Tama universe) it will be an old-man/woman, which isn't as fun as to look at as a Mimithci or Mametchi (or for that matter any adult charecter looks better then the old charecters).