I have been interested in this one girl for 5 years now. She lives next door, my mom knows her parents, not well tho

So 2 weeks ago I was alone at home and she was chilling outside. I went over and asked if she wanted to hang around with me. She agreed

Now were a taking a next step, starting dating. But my mom found out and she is ANGRY. She grounded me like bitch what the fuck?! She keeps shouting at me and telling me that “dating a 5 year old is wrong” whatever that means