Responses
She was over 20 and Joel was ~almost~ 17 when Jesse was born. That's why she doesn't tell Joel he has a kid, because he was still in high school. She just breaks up and leaves, then comes back when she is dying and Jesse is already 10. It's in earlier chapters.
Any adult who has sex with a minor is a pedo, whether they r a man or a woman.

I like Chase and Joel a bit better than the main couple and I like how the story's turning out. Also raising a teenager is terribly hard, and also also taking that into account I don't think Joel's such a bad father. He's not the brightest crayon in the box, sure, but Jesse is being harsh on him as well (he's a teen, and teens tend to act like that but I still feel like pointing it out, not many mother-father/highschool son relationships go super duper smoothly). Unpopular opinions much, but that's how I feel.