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:
http://www.pmags.com/300-gear-challenge

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.