Yes, at age 8 your tama will turn into an oldie but around age 12+ they can get married again. (He might be able to marry again sooner than that but I'm not too sure... but the matchmaker will definitely come in a few days).
It's a "Music Star" Version (V6, I guess), and he is 11 years old now. I rejected all the wives before, but now I want it. Nobody come to marry him since he turned old... T_T