In high school, it's def a little strange. The maturity levels are just two completely different places, even if either party tries to say they're not. One age is looking to the start of their high school carer, and the other age is looking at graduating and is an adult. It's also technically illegal. Once both parties are 18, a relationship between a 18 year-old and a 22 year-old isn't a strange, but in High school that's weird.
Just make sure the relationship is healthy, and that the age difference between you is legal in your state. Most places i have heard of have a 3 year law or something along those lines, so if its you taking part in the relationship, or someone you know, please do some research to make sure both partners are not putting each other at legal risk.