I can never tell when older men are flirting with me?

A delivery guy who regularly comes to my job always greets me and stuff and today he was setting down a bunch of boxes and was saying how hot it was outside ( which he’s been complaining a lot about lately and how he’s been sweating ) and how the boxes were exercise and he was like “you’re just trying to see me work out” implying like maybe in a flirtatious way. Was he flirting with me? I’ve never made a move on him or said anything I’m just nice. I don't know why he said that lol. Also it’s confusing because another one of my coworkers who I’m close with likes him and has been trying to get with him but she gave him her number but he’s not really putting any effort into her.
I can never tell when older men are flirting with me?
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