Guys, Why does my much older coworker stare at me so much?

He's 15 years older. I catch him staring at me a lot. The other day he was talking to someone else and when I turned around he was just staring at me with kind of a sad expression on his face? Whenver he sees me he makes a point to look.

From a guy's perspective, what do you think this means?
Guys, Why does my much older coworker stare at me so much?
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