Mouse knows of what she speaks; I personally love the Volt, though I don't use one anymore. (Way too much volume for any load I'm likely to carry.) Confused yet?

The volts are good, comfortable, well-built packs with beefy suspensions. (They used to have virtually the same suspension as the Aether, but I think Osprey switched the Aether to their "AG" system, which uses a trampoline-based suspension that ties into the hipbelt. I used that system on the Atmos AG, and found it wanting - so, you're warned.)
The Volts still have a traditional internal frame system. (I'm not familiar with your present packs - are they internal or external? If you like externals, you might want to look at the Atmos or Aether series.)

The Volts have a nice feature set, and their advertised load range is spot on. Personally, I believe the Volts could handle any load you'd want to carry at Philmont. They are also adjustable over a wide range of torso lengths, which may address one of Mouse's concerns about growth between now and then.

However, I'd also recommend that you take a good look at the ACT Lite series or the ACT Zero 50+15. Both are classic internal frames, also with robust suspensions and a great range of adjustment.

I'm one of those lucky people who find that Osprey and Deuter packs both fit me well. That highlights a very important idea: do not buy a pack without trying it on, filled with your own gear (not sandbags.) Fit is everything; get the one that works.

In my own case, I typically carry 15 or 16 pounds of gear (not counting the pack) for a weekend trip. At that load point, I can use a very light pack with a minimal suspension - and until recently, that was an Osprey Exos 48. My gear filled the pack; I had no extra space for a few days' extra food, or winter clothing. Also, I had concerns about the suspension's ability to handle more than 20 pound loads. Since I don't want to own 3 or 4 packs (although the manufacturers might think I'm nuts), and since I still plan on taking a few weeklong and cold-weather trips, I recently decided to go with a sturdier pack, and pay the weight price of the extra pound or pound and a half of a sturdier pack. After comparing a couple of other Osprey models (Kestrel 48 and Atmos AG 50), I settled on the Deuter ACT Zero 50+15. It had the best suspension I could find in a 3.5 pound pack, and the adjustable capacity was perfect: the basic 50-liter pack holds my weekend load perfectly, and the 15 additional liters of expansion will let me take those longer trips. In particular, I like the hipbelt - sturdy, but comfortable (more so than the Ospreys); when you tighten it, it stays put, with no sliding and hitching it back up.

I think Mouse is one of those people who can't wear Ospreys, but Deuters fit her perfectly.

You've got plenty of time, so shop around. Osprey and Deuter are good, but so are Gregory, Kelly and other models. Just don't fall for the "ultralight" thing, that you no longer need a "heavy" pack. You need a pack that will handle the weight and bulk of the loads you typically (or plan to) carry - that may mean a 3 or 4 pound pack.

Keep us posted, and ask questions as needed.