Anybody can be one. Make a dollar or two and you can claim you are one, too.
Thing is, you can’t just settle at being a “professional.”
You have to strive to be passionate about the things in your field.
Like myself personally: I love playing bass and guitar, and I also like tweaking settings on an EQ and then changing it up later when I find that I heard some things that needed to be changed. I might not be all that professional simply because I haven’t really made any money. I supplement my fledgling studio career with money I make working another day job.
But this paying for a future career with my own money is helping me build respect and knowledge about recording music. It is also helping me become more passionate about it all. I may not have the most equipment or even some of the equipment that the studios in town have, but at least you know that I will make the best of what I have and actually sit down and learn your songs and music so that I know what sound you need and how I will achieve that with my current set up.
As a bassist in a band, I would want the Engineer to care about the music we are playing and I would want the Engineer to know our music almost as well as we do. You aren’t just paying for the use of equipment when you are tracking and mixing and mastering your music with an Engineer/s, you are paying for their skills and knowledge, and if you are lucking, you are saving with their passion.
I want all of my fellow engineers and even friends working in their own fields to take advantage of their knowledge and passion. Don’t let being there be enough, make accomplishing your goals just a small part of what you aspire to be.