Bonsai isn't a plant species. Most inexpensive "bonsai" from nurseries are either chinese elm or juniper cuttings, both of which don't have a well developed root system yet and will definitely topple over under the weight of a young adult ball python.
Bonsai is just the art of pruning and shaping normal tree and shrub species over time to grow into the look of as if a miniature tree. Older or younger doesn't matter, the branches were meant to stay thin on top, and to have a thick base only. They're also meant to develop a shallow, flat root system anyway. A plant is only considered a "bonsai" when it's grown with the intent of keeping a shallow base and shaped into a tree. Otherwise, it's just a normal plant LOL.
Also, when most people think of bonsai, they think of junipers... Junipers need full sun and won't survive in a terrarium, and I don't believe they're reptile safe anyway.
A mature jade plant will hold up a smaller sized ball python, but still the new branches are risky under an adult, from what I'm guessing.
If you want a live plant, you want to find a plant that has a very strong root system in the pot (if you are keeping the plant in a pot), can live in low-light, and preferably has no branches.
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