How do you know if you actually like someone?

I've been single for quite a while, last relationship being in primary school (not sure what US equivalent is but ages 5-11), so basically not anytime in teenage years or present adulthood (24M), I've not even been on a random date with anyone in this time.

I've had my eyes on a girl at work for quite some time, we're good friends but recently these feelings started developing more and it's been that long since I've been in a relationship that I don't even know if they're real feelings or feelings I'm having because I've been single for so long.

How do I know if these feelings are real?