I'm sure someone will have a correction to this but; without knowing the source there is no way to know without destroying the tree. Counting rings is the only definitive way. However, you could reasonably estimate or make an educated guess. More experienced people will know more tell tale signs for specific species. I have read several books with very old trees, most of them were labeled with "estimated" or "believed to be".

Per your picture the top is likely one seasons growth. The bottom before it was chopped off could have been 5 years maybe. I'm have no experience with ficus. Maybe someone with propagation experience or who has owned one of these can give a better range.

Try this,google brussels bonsai nursery.they have ficus all kinds.they have a age of their trees posted see if you can see one that looks clost to the size of your tree.. hope this helps...john

You can bet their age estimates are consistently and considerably exaggerated, John.

AF - it's not particularly important how old your trees are, but it IS important how old they look.
It's actually considered impolite to ask an artist how old his tree might be, and most, when asked, will simply reply, "How old does it look?"

Your tree looks like it should be about 4-5 years old.

Sfhellwig - counting rings is very unreliable for tropical trees. They very often have several growth periods and 'rest' periods (often environmental dormancies) per year, and the number of periods can vary from year to year, which can cause several definable sets of rings.

Al

I have been told by a friend who travels to China where many of the commercial bonsai are produced that several cuttings of F. retusa will be fused together to produce one tree and that over time they heal over so completely that one cannot tell how many cuttings were used. Looking at your tree I would suggest that it may be one that was created in this manner and has not completely fused.