I am a male 17 5'5.5 with size 9-9.5 feet I bought some shoes which are a size 10 and feel slightttly big Could leaving space mean that my feet may grow into them bearing in mind my age?

It doesn't matter what size shoes you wear. Your feet will either grow or they won't. You can grow until you are 21 and your feet may well grow but not because you leave space in your shoes. Remember it is important to wear well fitting shoes.