Betty is an LI and will become (optionally) pregnant. Having two GILFs and not letting the players impregnate any of them...
She will carry her own child, don't worry.
Oldest woman to give birth: 73
Oldest woman to give birth, becoming pregnant in the usual and fun way: 65
Betty is younger
Not seeing the child grow up is another thing, but it won't be explored in My Dorm. The game finishes when the first kids are 21/22, so Betty and Meemaw will be still there in their 80s.
Until what age do you want them to see their kids grow? Obviously, they won't be around when the kids are 60+, but can be there well into the kids' 30s (their 90s). Spoiler:
My father isn't around and I'm 51.