My first generation Mametchi lived to 8 years old... and then the second generation baby took over. Do Tamas live longer if they don't have a succeeding generation?
No... and Yes...
The original Tamas on each unit will eventually die off (or go to Tamagotchi Planet), leaving the baby. Since the babies are twins of whatever gender you got, you'll NOT be able to mate those two until you get different genders on them again.
So, "Yes" the unit can mate...