Work History question

Hello all!

I fear I've gotten myself into bit of a tough spot with regards to my work history due to some very poor choices I made back in my High School years.

I'm currently 21, back when I was 18 I dropped out of High School and didn't get my GED at the time. I struggle to explain my reason for doing that beyond the fact that I was unmotivated and didn't know where my life was going then, plus I was just plain dumb. Over the past year, I've come to the realization of what an incredibly stupid choice that was, and I realized I need to make good choices from here on out and fix my life. I recently got my GED and passed easily without any real studying. Based upon the fact that I very, very much enjoy driving and traveling, and the fact my late Father was a trucker, I've decided I really want to get into the trucking industry.

A few days back, I went to Interstate Truck Driving School (A local and highly regarded CDL-A training school in my area) and explained a bit of my situation to them. They told me that I didn't necessarily need a work history to get a job driving, but from what I've read online, I suspect what they told me was wrong. Many of the trucking companies I've looked at have "a verifiable work history" as a requirement for employment, though a number of them do not have that listed. However, it seems like the general consensus on forums is that a work history of at least 3 months is needed. I have not officially worked for a company, but I've done a lot of stuff that could be considered 'work' on my own: Doing construction/home repair jobs for my Grandpa and my Mom, working for many other family members doing similar things, and fixing up a pickup truck I own. So I've not been idle in the past 3 years.

TLDR: Do all trucking companies require a work history? If so, what kind of work? For what length of time? And does it have to be full-time? I'd like to take a part-time job and work on getting my CDL at the same time if I can, which means full-time is out of the question in that scenario.

In any case, I could really use some advise here. I'm willing to do almost anything to get into the industry, and am very motivated to do so. Sorry for the wall of text, but my situation is a tptal mess right now, so it was needed.

Thanks everyone, and have a good day.