how do you know she is single and interested? well the answer is: you don't!! and you won't unless you ask or somehow figure out a way to get to know her better..i.e. by sparking up a conversation and taking it from there! so far you've got really vague assumptions of her age for example..so the only way to find out real hard facts is to make a move and spark up casual conversation and if she responds positively you're on the right track! good luck!