Can I being 19 to help fix my boyfriend’s papers or do I have to be 21?

There is no visa category by which a U.S. citizen may sponsor a boyfriend or girlfriend for immigration benefits, but a U.S. citizen may sponsor a spouse in a marriage-based adjustment of status application process. For that, the couple needs to be old enough for the marriage to be lawful where it takes place, but beyond that there is no age limit for immigration application eligibility. Of course, there are many additional details that determine eligibility; if you and your boyfriend are considering getting married, it would be wise for the two of you to consult with an immigration attorney who, after learning all of the relevant facts, would be able to advise about eligibilities, options and strategies, and then could offer legal representation in the often quite complex application process.