Ghusal

Salaah becoming qadha due to not making fardh ghusl after becoming baaligh

Q: If a male becomes baaligh by having wet dream and ghusl becomes fardh on him, but he doesn't know that in Shariat you have to perform ghusl after having a wet dream. So he keeps praying with just making wudhu and after 3-4 months of his puberty, he comes to know that ghusl becomes fardh by wet dream. So are all his prayers in these 3-4 months counted or does he have to make qadha?

While offering these prayers again will he make intention of praying qadha prayer or will he make intention of repeating the prayer (I'adah)?