Letting a old teacher follow you

So a teacher ( who never taught me and I never really crossed paths that much) from my old school which ive just graduated from and had just shut down, has requested to follow me on insta. Now I got told we cant follow teachers till we turned 18 and we’re 16 when we leave. Other kids in my class and other years follow him and he follows them back but I’m a bit hesitant with laws and getting in trouble. Is this okay? They are a really nice person and I know to report any dodgy messages and stuff but I want a second opinion