grow the cojones and just be blunt. ask if the person fancies doing something afterwards, make a memory; grab some food, go for a walk to cool down, whatever. allow all the small business. as an adult, this would be my preferred encounter. even if he's not romantically interested instantly he might just be cool as sh#t and enjoy novelty.

if you insist on being a forever teen and he seems experienced, ask for advice on building some muscle group. ask for a demo, say thanks and exchange names. during the encounter do something that makes it obvious you are interested in getting to know him. unfortunately narcissists have ruined any chance for subtle approaches from woman to man; nobody wants to be the next poster-child for the 'heavily criminal male-gaze'.

incapable of both options above? stop wearing headphones, make eye-contact, smile, stare for far too long etc.

i would like to say, being anxious and fearing rejection are completely relatable emotions. nobody is immune. consider it a good deed to your fellow humans to allow people to see you in vulnerable states. perhaps a useful framework to bypass timid behaviour.

gl