Before I did my first thruhike, I had only been backpacking for about a year. All my experience amounted to a handful of solo hikes in the Arizona mountains. My longest trip was my first - four days. My first AT experience was the day I started my thruhike.
In theory, more experience should translate to a higher success rate, but it doesn’t necessarily follow. A lot of experienced hikers do not complete thruhikes. A lot of total beginners succeed at their quest. The difference is generally in attitude and desire. You have to want the thruhike more than anything else. That will keep you going when times get tough - and they will. While getting some experience before you start at Springer will make the first few weeks a lot easier, and keep you from quitting the first week, it doesn’t make that much difference over the long run. While a lot of folks quit before Hot Springs, a lot of people also go home after four or five months. The reasons people quit are legion, but quite often it comes down to a question of will. How badly do you want to succeed? Are you willing to pay the price? Thruhiking is happiness (for me at least) - but it is also uncomfortable, frequently painful, sometimes boring, and often quite hard both physically and mentally. The rewards are great, but so are the costs.
Ginny