How to ask her

Well this girl I have been dating I'm 17 m and she is 19 f so we were talking about this and somehow she got turned on. I tried to put my hand down there but she stopped me in the middle and asked if it was right or not as im not an adult

it was the first time he's gotten that close, we've kissed and all, but that was no. I said you were fine with kissing and all and she said 'I'm fine with tha, but not this rn but after you're 18.'