How to let a younger guy know I'm interested?

Here is my dilemma: there is a younger guy at work I'm starting to notice. A few times we talked I got the vibe he might be interested. I don't initiate any conversations but the few we had he did and we both enjoyed it.
I got the vibe that he tries to impress me but at the same time he quite self-deprecating which I like because I'm the same way.
Since it's work I would have to really subtle because you never know. On top of that, I don't even know if he's seeing anyone.
What should I do to make sure he knows I'm interested?
I'm 42 and he's 35.
If you're going to post that I'm too old for him and all that, spare yourself some time and energy and just don't say anything.
How to let a younger guy know I'm interested?
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