How can I tell the older leaves from the newer leaves on my Yucca plants?
Younger leaves are normally smaller and lighter green in color.
I was wondering after the flowers fall off and the seed pods start, can I cut off the stems so the seeds won't develop? Will this hurt the plants? I had one plant, and now have four all with stems.
Once the stalk blooms, you can cut it off without harming the plant. You do not need to wait for the seedpods.
Yucca tops dead from winter damage. Dozens of pups growing out of trunks up to 3-4 ft. Can these be taken off and potted in an attempt to get new trees, or will this kill the main trees completely?
Yes, you can. This article will help with that: https://www.gardeningknowhow.com/ornamental/foliage/yucca/separating-and-repotting-yucca-offshoot-pups.htm
Do I trim to where the trunk grows without the leaves, like a tree?
It depends on what you want to accomplish with pruning. The part of the trunk that does not have leaves will not regrow leaves if you prune the leafed part away, but it will often sprout new branches. You should leave at least a few leaves on the plant if this is your intention to make sure the plant can still produce energy.
This article may also be helpful:
https://www.gardeningknowhow.com/ornamental/foliage/yucca/yucca-plants-care-and-pruning-tips-for-pruning-a-yucca.htm
I'd like to know if it's alright to cut the yellow leaves that are laying on the ground?
Yes, you can. This article may also help: https://www.gardeningknowhow.com/ornamental/foliage/yucca/yucca-plants-care-and-pruning-tips-for-pruning-a-yucca.htm
Above planted inside pool lanai. I am concerned as it is rooted right above my waterfall planter bed. Is this bad? Do roots grow down? Could they damage pool? It is growing fast. How tall will it grow? What are good plants to grow around a pool in a lanai with plant beds built right into pool deck?
Plant roots normally do not become harmful unless one of two things happen. The first is that they can't find enough water, but as this is a yucca, that is not likely to happen. The second is if the roots run out of room. Check periodically that the roots are not surfacing (a sure sign that they are out of room) and if this occurs, you may need to move the plant.
Anything tropical would be nice. I am partial to bird of paradise, brugmansias and elephant ears.
We were given a yucca still in its cloth bag and have not potted it yet (4 months ago). When should we pot it?
Spring would be best.
Here are some articles that you may find helpful: https://www.gardeningknowhow.com/ornamental/foliage/yucca/caring-for-and-landscaping-with-yuccas-outdoors.htm
https://www.gardeningknowhow.com/ornamental/foliage/yucca/separating-and-repotting-yucca-offshoot-pups.htm