Aw, that is so cute!
With parents, they 'assume' that they know what is best for us, but they really don't have a clue. Love has no age, and it doesn't have a religion.
It's totally sound if you want to marry him, when you're in love you know you're in love. I do suggest maybe opening up yourself to his parents. It seems that they only see you as a non-Indian girl but see your personality and who you are as a person.
For some reason, many people only see what they want to see. So, I think it is worth you know talking to his parents on a one to one level asking them why they are so against your relationship? His parents aren't going to be here forever, so I do think its worth having a chat with them!
Good luck & I'm so happy for you!