I joined PCA in around 1987. I started driving on track in 1988. Lime Rock Park with PCA. No karting or AX or anything related prior.
Transormative experience.
Arrived in Norcal in 1991. Lots of AX in the 90's, and time trialing, and racing until about 2017.
And instructing.
One of my old friends in the high-level AX space is Steve Lau:
https://www.youtube.com/watch?v=7pDeslmjf7g
https://www.youtube.com/watch?v=fJNm-U7wtQw
He and his wife are PCA and National Champs.
I was one of Steve's first AX instructors.
One of the first "reference materials" I reviewed for performance/competitive driving was the Skip Barber video "Going Faster." It was filmed at LRP in '86 or so, and I have been watching and recommending it since then.
In '94 I attended a PCA two-day AX school, and the leader of that had written a book called "Secrets of Solo Racing." We all got a copy.
Both reference materials are highly recommended.
My best student ever climbed the curve quickly, starting in a 944, then a 951 that was extensively developed over 5 year period. At the end it had about 360 bhp, a racing suspension and brakes, and big sticky dots. But it was still a 2900 pound street car.
Then we bought our current car, a 1950 pound 911 in 2001. Really a race car with lots of power and big sticky full slicks. And a 915. Very different from a heavy, high powered, front-engined 951.
She drove it in about 2-3 track days in Winter 2001-2002. First 2002 PCA time trial she started getting up on the tires in February 2002.
Second one, she got send overall in time trial at Laguna Seca in March '02.
Third one, she got TTOD at Buttonwillow. She beat the chief instructor. He had 2x the power in his very potent 911. He wrote "Secrets of Solo Racing."
As far as I know, only woman to get TTOD at a PCA TT.
Learned the basics, and focused on the craft.
For many, AX is a good place to start. A few events, then an AX school.
I bit less expensive in time and money than going straight to track events. And perhaps more readily accessible.