I'm 30 and I could easily pass for 35-40(rocking the Jason Statham haircut since 2013). If you are lucky, in 40 years from now you're gonna be on your deathbed thinking "damn, I should've always cared more about the opinions of women that didn't suck my dick."
Although similarly to Jezebel, a big % of TRP readers considers PUAs clowns, let me tell you what they would probably say to you:
Since you want to Game "under the radar" you can do what would be called creating masculine polarity through subcommunications: being verbally non sexual but escalating through subcomms. Practically, what subcommunication means in this case:
Eye contact
Distance between you and her
Vocal tonality/speed
The best videos to get these concepts are The Formula for Night Game by Richard La Ruina, Liam Mcrae’s Rapid Escalation and the PIMP by RSD Julien(you can buy or...whatever that product).
One more thing on eye contact:
ps: Just because it's good for your soul, do a super direct approach to an 18yo chick in front of the post wall chicks you mention. You will realize it's not as bad as you think it is even when it's bad.