Here is my 2 cents... this is not a retusa, but a tiger bark, the bark on the retusa is smoother and slightly grayish, not brownish like the tiger bark. Also, the leaves are slightly smaller and rounder.
The tree is decent, if you paid around $40 as stated above. Is it 13 year old... tough to say. Maybe if it was kept dehydrated and into a bonsai pot since it was just a string. Tiger bark grows stupid fast with the right amount of water and the smallest quantity of fertilizer.
Aerial roots look like aerial roots, I don't get where you think they look like buried branches. Aerial roots thicken rapidly as soon as they dig into the soil. Below is a sample of my tiger bark aerial root development.
Aerial root on the front-left was but a string APR 21, below on AUG 21 already 1/4" of the trunk size.
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Here on NOV 22
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Strings on AUG 21
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almost 1/3 the thickness of the trunk on NOV 22
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