I just noticed this thread, and apologize in advance insofar as I haven't read every reply --- thus I might be highly redundant coming in late to reply just to the original post but ...

whiteblaze.net is the clear, one-source place to learn about hiking the AT.

Why are you going south? I suggest that you start north, and definitely do stop about, what, 30 miles in an Neel's Gap and get the "gear shakedown". Yes, they sell gear there, but I watched them go at the shakedown process (by employees that have thru-hiked the AT themselves), and it's not a scam to sell you lots of gear.

Going SOBO (SOuthBOund) is just tougher, I think. You start out climbing Katahdin, and even after I'd hiked 2000 miles or so to get there, that wasn't all *that* easy of a climb. And then relatively early on you're into things like the Mahoosic Notch and most importantly the Whites --- those mountains will kick your butt if you're not in shape, and in fact they'll do some of that anyway.

I'm not saying that you can't do it SOBO, but I think your odds of success go up a bit if you walk northwards from Springer.

Alcohol stove vs. MSR white gas: take the Alcohol stove. Definitely. Make one yourself from a catfood can, it's not hard and for that hike it's way better than a crazy heavy stove.

Old cheapo tent: depends on what you have, and what your budget is. Also depends on what time of year you're going (and in what direction). I personally slept mostly in shelters but I started early so there was little competition. In that context, a really light tent that I carried but rarely actually used was a good choice.

Look through the old $300 challenge article for ideas on how to get decent gear on the cheap:

Look carefully through whiteblaze.net for the various articles, not just the forum entries, and you'll get lots of ideas on "what to do next" to prepare.

I'd also strongly suggest a shake-down hike of at least 50 miles after you've got your gear mostly together.

So long as your overall health is good I wouldn't worry about age; I was over 50 when I thru-hiked, and I've hiked with guys well into their 60's that kick my butt on the trail.
Brian Lewis