Do any of these people telling you this have ANY experience hiking? I'm going to wager "no". How much advice you take from people completely ignorant on the subject matter is up to you but IMO your goal is not only achievable but is easily achievable.
When I started the AT 4 years ago, I had done a decent amount of day hiking out west carrying only a camel pack and some snacks. I had car camped but never overnight hiked where I had to carry everything. I did a decent amount of research online especially in what to bring / not bring and what gear to buy since I had none. I bought the gear I thought was reasonable, loaded it up, went to a large state park area an hour away, parked my vehicle, and did an overnight out and back shakedown. I think I walked about 14 miles with all my gear, made camp, didn't sleep worth a damn, got up the next morning and hiked back to my vehicle. I took notes and made some gear adjustments and after that one night shakedown, I booked a stay near Springer and did my first section from Springer to Gattlinburg (200 miles).
What I learned on my shakedown and first section:
- My back was KILLING my shoulders after the shakedown. I was wearing it wrong. It needed to be higher on my hips and the hip belt much tighter.
- Trekking poles are worth it. I thought they were for old people or people with bad knees. I never used them day hiking. I was wrong. After a few days without them the downhills were brutal on my knees.
- Footware is crucial. I swap out my socks mid day and let my feet air out at lunch.
- Weight is a big deal. You probably don't need all the stuff you think that you do.
- The miles aren't that hard if you are in OK shape and carrying reasonable weight. I my first trip I found that 10 miles a day leaves a lot of time for goofing off. 15 miles a day is a day of hiking with long breaks. 20 miles a day is doable if you keep at it all day, start in the woods, and sleep in the woods (no town or shuttle). This is from a mid 30s guy in decent shape.