How do you deal with students trying to hit on you?

I work as a researcher+teaching assistant at a technical university. Most of my students are men in their 20s and at least 60% are my age or older. I've tried my best to appear mature but they do not understand it. They keep asking me to solve doubts after class and try hitting on me. I get tons of mails from them asking me useless stuff and suggesting that we should meet somewhere outside the campus to 'discuss' studies. I have told the authorities but they're not ready to make exceptions for me. What are some things I can do to stop it?

How do you deal with students trying to hit on you?
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