How long can a 25 year old go to jail for dating a 17year old? He can go to jail for dating beause he is but I want to know how long will he get? If they get married can that stop them for chargeing it? When she is 18?

What state are you in, if the US? Laws vary by state. You can look up age of consent or ask here, below.

There's no jail time for dating, only for sexual contact. And her parents have to approve of the dating, of course. Which state?

'he can go to jail for dating beause he is ' can be taken two ways. He can go to jail because he is dating or he can go to jail because he is going to jail.
If he is going to jail and your only question is for how long, we can't know that. There's just too many variables about the whole case, not just what state they are in.

He is already in jail for dating her.
Its in Washington state the parents didn't aprove of eathir there the one who sent him there

he is already in jail for dating her.
its in washington state the parents didnt aprove of eathir there the one who sent him there

Parents cannot send someone to jail for dating. They can report a violation of the law to the appropriate authorities (police or prosecutors) and they can investigate, decide whether laws have been broken and file charges. An arrest can then be made. So, if he is in jail, it is because he is accused (or convicted) of violating some law.

You really need to provide more info if you expect some help. Please answer these questions:
1) Was he just arrested or has he had a trial and been convicted?
2) What was he charged with (arrest) or convicted of (trial)
3) Was there sexual activity involved?

The age of consent in WA varies by circumstances http://blogs.seattleweekly.com/dailyweekly/2011/05/why_is_16_the_age_of_consent_in_washington.php

As for getting married, until 18 she needs parental consent.

P.S. why are two accounts being used here?