Taking back birth name

I know I am probably out of my realm here but, my 19 year old biological son is in a pickle and I'm trying to seek answers.His biological father chose not to be in his life, for various reasons, from very early on. Anyhow, I had married shortly after my son had turned a year old and my husband at the time was the only father my son ever knew so, after a year of marriage, I allowed him to step parent adopt my son. I thought I was doing right by my child but, years later, the marriage ended up being a whole mess of mental illness and abuse and ended in a very difficult divorce. My ex-husband had completely walked away and abandoned both his adoptive son and his younger biological son. For 8 years my children did not see or hear from their dad until I ran into him one day. He then came back into their life only to turn around and leave once again this last Spring. My adopted son had even moved in with my ex for about 2 months trying to gain a father-son relationship with him, but his dad still wrote him off, changed his number blocked his own children on Facebook, and cut complete ties once again. So right before Christmas my son sat down and had a heart to heart with me asking about his biological father. Long story short, over the holiday vacation my son took it upon himself to meet the family he's never met before. He was embraced with open arms and quickly became close with his cousins. He even spent a few nights over at his aunt's to get to know them all better. His bio father works on the pipeline and is out of state a lot but actually called work to tell them he would be running a few hours late just so he could stop in at his mother's house and surprise our son. So now, I am faced with a question that I do not have an answer to. My son is currently working to get his aviation license as an airframe and power plant technican and has entered into the delayed entry program for the United States Marines. He was supposed to meet with his recruiter today but texted me very late at night from up in his room (lol) expressing to me that he really didn't want to sign any official documents until he changed his name. His desire at this point is to change his adopted name back to his biological birth name. His biological father was a Marine and he wants to follow in the family footsteps. I am all for supporting my son's decisions but, I do not have a clue on how to reverse his name. I would not know the first person to call or any of the steps he would have to take to make this possible. I guess this is a two-part question but, I don't know how to look at it from an adoptee's point of view so I'm reaching out to everybody on this forum....Is it for wrong for me to think that this might be too early of a decision for my son?And if this is something that he truly wants to go through with,does anybody know the proper steps you would have to take to make this possible?Any advice would be great. Thank for taking the time to read.HL Joe