You can ALWAYS mate Tamagotchis no matter how old.
Yes, use the Love Potion. If you have two Tamagotchis,
connect the one using the Love Potion. If you have two Tamagotchis that is...
Anyways, if Otokitchi (Old Timer Female, Otherwise called Matchmaker) and Ojitchi (Old Timer Male)
mate, they make a seceret character. After they have their baby, it will evolve very fast
until it's Adult, then it's the Seceret Character.