How young is too young?

I've been texting and talking to this girl that is 18 years old... I'm 22... Is that wrong? Sometimes I think I'm an idiot hahaha. Maybe I'm wasting my time, but I'm not doing anything wrong by talking to her. I text with a few of my friends that are girls, but it's usually just a friendly hello, what are your plans tonight, ok I might see you out later. She actually gave me her number and texts me all the time. I'm not even really sure where she stands or what she wants. I'm just being friendly and letting her work things out as she wants. I think she's just lonely from a recent break-up, I know how that goes. I have sympathy for her, she's a sweet girl who deserves to be treated right. She's young though and I don't know her well enough to judge her intentions or emotions,  I'm just going with the flow. I really don't have any romantic interests right now, so why not talk to her? I try not to initiate conversation too much simply because I don't want to be the older dude, blowing up a girl's phone. She's funny though and honestly I enjoy chatting with her. Still, every once in awhile I get a feeling that I'm being a fool, maybe we both are. It's a day for fools anyway haha.