looks like a tree my dad grew from plating a grapefruit seed for fun . I remember it having thorns also! Not sure , but it looks a lot like it
Maybe a Quince. Did it bloom in the spring?
im just noticing it in my father in laws back yard...he will grab anything up and plant it as he loves gardening. He has lymphedema and cant care for them so I try to help out..its very difficult because he only speaks spanish and I know NONE of that! So I will try to find out what he calls it!