I think, the word Professional gets bandied about way too often...
I began from two separate paths; I liked photography and also cars, so mixing the two interests i purchased some cheap cameras and started taking photos...
Now, while the photos i took in the first few years were pretty useless (and i could see this), it drove me to want to improve and take shots like i saw in the 'magazines'...
As i got older and owned cars, i became involved in car clubs and began attending a lot of racing and show events, and my photos got better...
Eventually, after probably 20 or so years of taking snap shots, then average photos, then reasonably good photos (just for me), people began to ask if they could buy images of their car...
By then, I had an extensive magazine collection and was beginning to be interested in writing about cars too, so i took the plunge and submitted some photos to a magazine (which they were happy enough with to purchase). They asked for the vehicle details and i offered to write an accompanying article (which they also liked, bought and published).
This became a regular 'second job', and i produced articles for automotive mags for several years, including covering events. This exposed me to motorsport photography (which i wasn't very good at to begin with) and so i started learning how to do that too...
My 'main job, at the time, was for a local newspaper, in the pre-press department, laying up ads and, luckily for me, they were just upgrading their software so i got paid to learn how to use Indesign (I'd already been using photoshop for a few years)...
I was eventually asked (when an editor left) if i wanted to step up and work full time for the magazine, as editor and main writer photographer (small mag, smaller budget) which i accepted. It lasted a few years and, as many publications do, eventually failed through mismanagement (by the owner, not me)...
I then moved on to a job for another magazine, but in production (basically, they were another cheap arse mag owned by a rich businessman) as the graphic designer...This lasted only 6 moths as he liked his money too much and didn't like to part with it (including paying staff)...
I also did a stint as a Journalist for a heavy transport industry mag for a while too...
Now, i just produce advertorial/editorial features for a few local newspapers every now and then, and the photography is back to being a hobby...
Apart from the (minimum) training in Adobe InDesign at the 'paper', I am self taught, literally, through trial and error and customer critique.
Am I (or was I) a professional? I don't know, as i just refereed to myself as a photographer (or designer, or writer)...I left it up to the CUSTOMERS to decide if I was professional...