Great advice from both Thijs and Baja.
The younger part of the trunk may root quicker, however it's not necessary to cut the older part of the trunk away in order to stimulate rooting in the younger section above. I believe it's better to let the plant decide where to root from. Cutting trunk away seems like it only decreases the amount of 'energy' reserves the plant has.
I also feel like soil is not really necessary at first–I've had plenty of Aloes develop aerial roots when the underground roots are compromised. I like to be able to monitor the progress and condition of the trunk. Once you see root initials, it's safe to pot the cutting up.
What I do feel is critical is to reduce stress on the plant during the rooting process. Give the cutting bright light, and no direct sun, unless you can limit it to one or two hours in the early morning. I have had stellar success by providing a tent-like enclosure over the entire cutting in order to raise humidity. This works wonders, even with large Aloe and Yucca stems which would seem to not need it. The enclosure should allow a slight amount of air circulation. I've used a tightly-sealed clear plastic bag, but I open it every couple of days in order to refresh the air. Balance air circulation and moisture so that there is just a little condensation on the inside of the plastic tent or bag in the mornings. If it gets too wet inside, just let it breathe for a while to dry out. In Zone 11, the conditions are perfect for rooting an Aloe over winter.
You can edit your profile to include general location and zone information in the header of your posts. There will always be follow-up questions, but that basic info will help the other members offer better and faster advice.
