How to pursue a woman and know if she is not just being friendly?

Anonymous
I still haven't figured the dating scene out with women. One minute I think I do, other times I don't. Some folks might think I am trolling, but I am not because I haven't found a way to figure this out. One recent piece of advice I have gotten is that I might be coming off too strong. I always thought to go in, try to make some small talk (yeah hard for me to do with random person, but I still try), then ask for her number, and try to setup a date. I try to be straight up and let her know that I am looking for a relationship, maybe after the first date (this is something recently I have been doing). My end game is that I want to get married some day, but can't help possibly coming off as creepy/desperate, based on the whole might be coming off too strong. I tried to talk to this young lady at my job, and I thought she was into me.
Whenever I asked her out or tried to flirt with her she would just stop talking and clam up. She doesn't even really talk to me like as before. When we would see each other she would be so excited to see me, and I mentioned to hang out she seemed opened to doing so. The first time I tried to do so nothing, hence I backed off and waited a few months. We kept on talking and I was getting some more information about her like the music she likes, so forth, and we were vibing. So I tried to flirt with her or so I thought, and setup up something again. Like before she just clams up and stops talking.
Now I just stopped and moved on and there is this other young lady that has caught my eye. The thing is she is a lot younger than me as in 23 and I am 36. Some of the things she does I pick up as possible interest, but after the other young lady she can just say she is being friendly. So I am not sure if she realizes I am interested in her (I can't even think or talk straight around her).
I say all this to find out how to really see the difference of friendly/interest? Then how do I pursue her properly?
Updates
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The reason I ask this question is due to being told recently, I might be coming off too strong. Then the same folks who gave me the advice is to just talk to her as friends, and see if she comes closer. Comes closer as in show more concrete signs of interest. I just don't know if I will really pick them up, and I am so scared of moving too late.
How to pursue a woman and know if she is not just being friendly?
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