How to become less approachable?

For the past 2 months lots of older men have been consistently hitting on me. every time I go out on my own to a store, mall, park, friends place etc. AT LEAST one older man will speak to me. Most of the time they're asking personal questions such as schooling, age (when I tell them all they say is I look much older and still don't back off), where I live, etc. Some would even have the audacity to ask for my number after! Rarely is it ever just a casual chat which I wouldn't mind since I'm a friendly person. The reason this bothers me is because I don't really want to be seen like that.. I don't even wear skimpy clothes, it doesn't make sense! I don't know what to do since I don't have a heart to tell them to "f*** off". What should I do to become less approachable?
How to become less approachable?
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