There are a lot of question on Chemistry, Physics and Mathematics SE that are related to IIT-JEE. For those who don't know it is an Indian examination in which around a million students participate each year. It would be really helpful for JEEaspirants as we will be able to sort through the questions related specifically to IIT-JEE
I agree that there are a lot of questions related to JEE on this site (I myself asked a lot of them!). However, I disagree that we should create a specific tag for them.
Tags that don't describe the actual content of the question are called meta tags. Meta tags are discouraged on StackExchange for a very long time now, see this blog post from 2010. Examples of other meta tags would be beginner or (drumrolls...) homework. As per this description, iit-jee would be a meta tag that doesn't describe the actual content of the question.
So, while I do agree such a tag can certainly help JEE aspirants filter questions as per their needs, that tag simply doesn't fit into the SE model.