Girls, My girlfriend is 10 years younger than me and people are giving me flack?

I love my girlfriend and she loves me. She's 19 and I'm 29. She knows I'm 29 and she's ok with me being 29. She's of a similar culture to me and we met and we are dating. I've met her parents they're OK with me dating her. Everyone that's concerned is fine with it. But some of my friends said I was a sicko and one random old guy said I should be disgusted and laughed at me for holding her hand in public. Another guy came up to me and her in the park when I was just kissing her and I lay with my head on her legs, he was like 45 and he said something like "can you two get a room?" What's with all this flack?
It's legal where I live but I cop flack. Why?
Girls, My girlfriend is 10 years younger than me and people are giving me flack?
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