Hey Saraha,
It is not the species -any woody plant can by the right person, be turned into a bonsai-. Granted, some species are much better than others, and for some you will need to have a very large tree to be realistic.
In your case it is mainly about age and development of the branches.
The plant below is about 10 years old, and I gave it its first wiring about 8 months before the picture was taken. I would not call this a bonsai, as the branches are sparse, there are primary branches and some secundaries but they need development. And overall, this does not yet give the impression of a mature tree.
Compare it to the plant that you and your friend have. I would venture a guess they are max 5 years old from cuttings. I do not believe for a second that these are 20 years old, based on the bark, the young branches all over the tree and the species. It is NOT a problem if a plant is young. Sellers often inflate age because they assume that that will increase the value. And many people new to bonsai also thing so. Unfortunately, it is the IMPRESSION of age that is adding value to the trees.
I have a juniper that is about 20 years ol, grown from cuttings by a person I know well. Look at the impression. If I were to tell you the plant was 50 years old, you might believe me based o the rough old bark and dead section, right?
Bonsai is an illusion. And certain minimal aspects need to be met before something can be called a bonsai.
None of my trees are bonsai by official Japanese standards. In the west we are a lot more accepting, but still.. A basic minimum is there. It needs to really have some tree-like aspects which the plants you and your friend bought do not have.
That also does not matter. It is after all just a label and you can still enjoy it even if it is not a bonsai. Just because the cheese you buy is not an official Gouda Cheese, does not mean it does not taste good!
