Flirt with them and see what happens. Send them poems. Give them tons of signs that you notice them in a special way. Compliment them and slowly touch their hand, arm, legs, (whatever they feel comfortable with ) when you talk with them which are hints that you like them. If they act the same, then it's a no go, either they are not feeling you or they have something going on and you're not invited.
If they flirt back you got your answer. If they are immature tell them you need someone who will understand you and they are real to themselves and others versus someone who pretends to play the role "I'm not feeling you but inside they want you bad".
There comes a time in your life when you just want the truth and nothing else matters until you know it. We're not getting younger so never give up on you quest for love.