What kind of body language/signs would an older man give if he's interested in a younger woman?

I am very attracted to an older man. I'm about 15 years younger than he, and I can't tell if he's interested or attracted to me. The only type of body language I've picked up on is eye contact and a smile here or there.
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I saw him last week and this time I believe I received mixed signals. One minute looking my way, the next minute acting as though I was not present at all. And then, out of no where he randomly began to converse with me? Men, seriously help me!
What kind of body language/signs would an older man give if he's interested in a younger woman?
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