I don't know if you've ever seen that chart- its a record of what is the ideal age of women according to men. As it goes from 18-50 year old males, their preferences stay within the range of 18-22 year old females. their interest in young girls is creepily common, and these men essentially want someone they believe is easier to manipulate and someone they perceive to be 'dumber' due to their age. They find it hot that someone is 'barely legal' and still in school. They use the 'you're so mature for your age' as a buffer to what is basically paedophilia, so it raises less red flags for you when they speak to you. Don't worry about wanting to flirt back, the creepiness is from their end. Idk about you, but for me I just liked the attention and I thought it was cool that older men liked me at 16/17, but now I'm 20, and if I imagine myself at 25/30, I would never even think of going after a teenager. Honestly, if you really want to, harmless talking online for a bit is fine if you want to entertain it for your curiosity, but things like this escalate really quick, so id recommend never reciprocating in person.