And I mentally managed to get the child's age to -1.8 years

, which is indeed possible for the african elephant, so I figured daddy was in Africa. Lol, should never use my head unnecessarily...
Btw, no need for an eq. system really as six years from now, if child then is c years, mother will be 5c years. Since the difference remains, 5c - c = 21 years, i.e. the child is then c = 21/4 = 5.25 years, which translates to -0.75 years now.
VAXman, thanks for twisting our brains

Hoping for followers. I might have something in a drawer somewhere...