crushes are harmless.There's nothing wrong with crushing on someone older অথবা younger...up to a certain age.I think up to 10 yrs older than আপনি should be old enough though.
It's a crush, there is no age limit. When I was a teenager I had crushes on older men, but there was no harm in it cause nothing would never have come of it.
Of course not! I had a crush on someone who was in 11th/12th grade while I was in 8th/9th grade. Plenty of people have also crushed on celebrities, and even had আরো than one crush. (Which applies to me as well) It's totally normal, there isn't anything to worry about ^_^