I bought a Ginseng Bonsai three years ago and decided to let it grow out into a tree. It is definitely flourishing, but I am now questioning if the top will become too heavy for the base, and if this could be bad for the plant. Any information is appreciated Right now it is about 23 inches from top to bottom, and about 21 inches across at the longest point.

I think we should not use the word 'Ginseng' and 'Bonsai' in the same sentence, but other than that:
I don't think it is possible to judge that from the text only. Do you have a photo ?