Miriam ., The Prophetess - Miriam's age

My dad and i were learning Masechet Megila page 14, A-
The talked about the 7 prophetests and it said Miriam was one of them, here is where my question came up, how old was Miriam when she made her prophet her mothers baby would save them, she must have been young, he kised her on the head than atted her. But she couldnt have been young, because she was Pua, the Yoneket, how old was Miriam?