The TamaGo has this glitch on it where every time the clock reaches 7.00 AM it will age whether or not it's been a day. That may be the case. Ninety six hours after it has become an adult (age 6) it can mate. Your TamaGo's age counter may say 7 but there is a possibility that s/he's about 2-5 in reality. You could check back each day to see if it comes up, and when it does, you can send it off to date place.
It's a good idea to try and keep the clock on the correct time so it doesn't happen, then it should age properly.