Not the AT, but the PCT, back in '06.
Someone up thread commented about the PCT being harder, physically, than the AT. Not true according to the AT vets I met on the PCT, so having done both, they'd know.
The AT is an "Eastern" trail - it's meant for chest beating, not as a practical transportation or getting from "here to there" route. It goes straight up and down hills, without switchbacks, at steep grades. The PCT is built as Western trails are - that is as a means to get from "here to there" and move things - it's graded for stock travel and liberally uses switchbacks to ease the grade. It also doesn't go to the top of every hill it passes, unlike the AT. Different characters.
The PCT is harder than the AT logistically. On average, towns are a lot further apart. 100 miles from supply to supply are not uncommon. Heading north from I-90, the PCT crosses 5 roads for the last 250-ish miles to Canada. Being deep in big "W" Wilderness is common - rescue is NOT around the corner for the unprepared. Shelters are for sissies - there are only about 3 on the PCT, not every 5 miles like the AT - carry your own tent / tarp.
Doing the self mailing of supplies isn't an issue or all that complex on either trail - use the information that is available for the trail you're interested in and you'll see it's easy.
As Mikedom said - expect it to be sub 30 and 50+ years old folks. Very few, relatively speaking, in that middle age range.
If attempting a thru, don't ever, EVER think about your finish, be that Katahdin or Monument 78 until you're less than a month away from it. Worry about getting to the next town stop, the next supply, the next shower / clean clothes / real food on a plate. Only look that week ahead, since standing in Agua Dulce (mile 454 and having taken you 3 weeks to a month to get there), Canada is an overwhelming 2200+ miles and 3-4 more months away. Worry about getting to Mojave / Tehachapi instead (and from there, to Walker Pass and Kennedy Meadows, and from there, through the High Sierra to VVR, etc).
In re the pros / cons of section hiking versus thru:
Section Hiking
Upside: Section hikers can cherry pick the sections. They can pick the best times of year for each section. They don't have to quit their jobs (usually). Easier to slow down and do side trips.
Downside: You have to get into shape every time you do a section. Logistics are a lot more of a headache. Don't get the comradery like a thru.
Thru Hiking:
Upside: You do it all, in one fell swoop. After the first few weeks, you're in trail shape with hardened feet. Fly to start / fly home - be all end all of personal logistics. Lots of new friends. You're a thru hiker - 'nuff said.
Downside - you have to keep moving so only a limited time for side trips. You have to take the sections when you get there, instead of at their optimal time of year (snow in the Sierra in June, versus doing in August, for example). The less than scenic sections that you have to hike thru to get back to the real good stuff (although this is STILL better than working).
Of course, YMMV, HYOH, IMO, free advice being what it's worth, 2 cents, yadda, yadda, yadda.......