Don't respond, that ends that! He's way too familiar for someone you hardly even knew back then.
You guys are all right. He was a freshman, I was a senior. His sister was a casual friend, a junior at the time. I believe we got to be 'friends' because I was something called a "Trusted Reader" in high school...junior and senior kids who were 'good kids' were chosen to go to the middle school and correspond with 8th grade writing students...the kids wrote in journals each day about anything they wanted to, and we could comment, praise their writing if they wrote stories/poems, etc. Was supposed to build their confidence and also that way when they were freshman and the juniors became seniors, they would 'know' some high school people.
I doubt they could do that anymore, too many inappropriate possibilities! In fact, my first boyfriend ever, hot plumber, was a trusted reader. I dumped him after an 8th grade girl put her journal in MY pile to read...full of flirtatious innuendo between her and him. (Your butt is like butter, are you horny, etc etc) I turned it in to the 8th grade teacher and he got fired from the job. And I dumped him. But I digress.
Anyway I recall this guy was one who wrote to me back in the day. Well, once you are married I am no longer available for daily conversation about personal things.