17 dating someone 22? Please respond!

So, I am 17 years old and I have been talking to a guy that is 22 years old. He is a great guy. He lives with his 70 year old grandmother and takes care of her. I have strong feelings for him. I am just curious of people's opinions on this. Nice or harsh. Also, if I do begin to date him how should I tell my parenta about his age? Please leave responses!