Immigration adjustment procedures for immigrant who came to the U.S. as a child

One major issue in this case will be whether your boyfriend was lawfully admitted into the U.S. or not. Whether he came into the country on a visa and has overstayed the visa, or whether he entered without inspection will make a difference whether he is able to apply as an immediate relative to get his green card. Additionally, whether any other type of immigration petition was filed for your boyfriend is also important. One of the major concerns is that your boyfriend has been accruing unlawful presence in the U.S. since his 18th birthday. Once a person has accrued more than 1 year of unlawful presence in the U.S., they are then subject to a 10 year bar to re-entry into the U.S. if they were to leave the U.S. and attempt to enter again. Accordingly, the challenge in this case is to have him apply for his green card while still in the U.S. Whether this is possible will depend on more specific facts.

If you seek advice on your case it would be a good idea to discuss your case with an immigration attorney. One thing to keep in mind is that you want to avoid committing any sort of immigration fraud against USCIS as this could ruin your boyfriends chances of any future legal means to reside in the U.S.

Note that as immigration law is federal law, any immigration attorney in any state in the U.S. can assist you with this matter.

You face being informed that he will need to Consular Process in Mexico. Upon return there, a 10 year bar to re-entry (based on overstay and/or unlawful presence after age 18 for over one year in the U.S.) could be awaiting you. There is a waiver for a spouse of a USC (United States Citizen) based on extreme hardship to the USC.
Due to this, you should document his entry (visa, EWI [entry without inspection]), time in US after age 18 (minor's time tolled), and such matters as: no criminal record? no public benefits? deported? Claimed to be US especially on I-9 form? married before? As much fact gathering as you can do will help before you proceed.

You should NOT JUST MARRY and FILE. It would be prudent FIRST to discuss the facts of your case with an immigration attorney, and yes, it is a federal area of practice, so an attorney may be licensed and practicing in other than the state you live in (However, when there are family law and criminal matters) that intersect with state laws-- that can be a factor in coordinating with the other lawyers on the case. You should be aware that you could face Consular Processing and being apart for approximately one year, and a waiver that may or may not be approved. You may not want to marry and file until a given time when you would be ready to face the process and best and worst case scenarios. You can't just adjust status in the US unless the USC marries an alien who is eligible to be married under the law(s), and entered pursuant to a valid visa-- and did not violate various immigration laws-- including entering with a visa other than K when intending to enter to marry and immigrate.

When you will get married you husband would be able to get the green card thought you by filling an adjustment of status application you can go to www.uscis.gov and read the procedure for adjustment of status
usually it take 9 month to get the green card. First he will get the temporary green card for 2 years and then 90 days prior to expiration u have to file for permanent

Given your age, you also need to be thoughtful of the Affidavit of Support.