Sorry, I’m with the mom on this one. The age difference does matter. Her daughter is only 14 and under age of consent. You are 17 and should be dating women your own age, not a kid. The fact that you were leaning on a 14-year-old suggests to me that you are immature or that you are having trouble navigating relationships with others your age. That is your problem, not the mom’s decision to block you.
It is the mother’s job to protect her daughter from getting taken advantage of or for getting sexually involved too early. It shows responsibility and good judgment on her part that she did her job. I also suspect that the girl is maybe a little relieved and that’s why she isn’t taking her mother on. She knows on some level that she is in over her head.
You can lump me with her mom and decide we’re both unfair — or you can do your personal work so that you can be comfortable with other juniors and seniors in your high school. I hope you will choose to work on yourself. Do consider seeing a counselor to give you the support and guidance you need.
I wish you well.