1. It's just fine. Usually Tamas become adult characters between ages 2-5. They have to have been at least one day as an adult to mate, though.
2. When your Tama has a baby, that night it will stay with it. Then it will stay with the baby for the next full day. It won't be until the night of that full day when the parent finally leaves at 12:00 AM. These events will occur in this exact order if you do not pause your Tamagotchi at all during this time.
3. It depends on the way you look at it. If you consider "rare" as something that you can NOT buy at the shop, then beef is not rare. What I'm saying is that beef can be purchased at the shop on a regular basis, so it is not particurally (sp?) rare if you recieve it from the King.
Good luck!