Ok I am a 12 year old girl and I use to go out with a 17 year old boy but everybody say that it legal

Anything of any sexual nature, including kissing, is illegal in many places of the world. Since I don't know where you live, I don't know if it's illegal there.

Most 17 year old boys aren't interested in 12 year old girls. They see them more like a little sister. You are too young to be dating, don't rush growing up. It's not as fun as you think it is.

"Going out" is a vague term. ANYTHING a 12 year old does is up to her/his parents. The legal part is all about the older person. In the US, each state has their own laws.
Most states have what are called Romeo and Juliet laws too, that are based on age difference, not just age. But I don't know of a single US state that includes age 12 in any way for a lesser charge for the older person. 12 is TOO YOUNG to be 'dating' anyone, especially someone older. Go places in groups. You have too much to learn.

This is the one part of life where you can be considered guilty without any evidence. If your parents want to have the 17 year old charged with something, whether statutory rape or risk of injury to a minor, they can. Risk can be just about anything they consider dangerous, like going to party where drinking is going on - ANYTHING. And if the charge is statutory rape (sex with someone below a certain age, whether willing or not), the conviction puts him on the publicly viewable sexual offenders registry for life.

The only people who can approve or disapprove of this relationship are your parents, and it doesn't matter whether it's legal or NOT, or where you live.

So do they know who you are dating?

Your parents are who you need to ask. Do they know you're seeing this guy.
I don't know what a 17 year old would see in a 12 year old any way.

At 12 you're a child, and therefore are subject to what your parents allow. If they're okay with you dating, you can date. But they have the right to say no. So do they know that you're dating? Do they know that you're dating a 17 year old boy? Do you know what the word dating means?

Now, some parents are morons and let their children do whatever they want. That's why there are also laws to protect children. At 12 you aren't legally allowed to give consent to anything sexual. But, your 17 year old boyfriend can consent, in most States and Provinces. He's of legal age. You are not. So, if the two of you did anything sexual, kissing, or more, he could go to jail for statutory rape, or grooming a minor. Do you understand?

So you have a few issues here. One is that you're dating a boy that's almost a legal adult, and you're not even a teenager! You're a child! That's sick. What does a 17 year old see in a 12 year old? You're both on way different levels of maturity, no matter how mature you might think you are for your age. So why is he interested in you?

You have to talk to your parents about this. If you've done anything sexual with this boy, he can be charged and he can go to jail. It's not even up to you because you're not old enough to legally consent to anything the two of you did if it was sexual.

Dating isn't illegal, but you need to know the definition of dating. It means going out somewhere together, or spending time together, maybe holding hands. Once there's anything sexual involved, you are no longer merely dating, you're in a sexual relationship, and that's where the law can and will put a stop to it if you're not of age.

In other words, stay away from 17 year old boys. Heck, stay away from boys period. You're too young to be doing any of this. Talk to your parents about this, and slow down. You have the rest of your life to act like a grownup, but right now you're a child, and you should act like one. That doesn't include dating!

The only thing I have to say is steer clear from this 17 y/o and focus on someone your age.

If there was any touching, even over clothes of a sexual nature, the boy could be charged with various crimes, depending on the exact laws of the state.

If there was any actual sexual touching without clothes or actual sex, those criminal charges could put the boy away for years.

Also there is an entire maturity issues.

A 12 year old, would need permission of her parent or guardian to date and without that permission it would be illegal.