Synthetic oil will not adversely affect any engine at any time, with one minor exception. Break in on many (not all) engines should be done with non-synthetic oil, just to let the rings seat to the bores. You're past this point with your bike, so no worries.
Some synthetic oils have a high detergent content and so will clean out a lot of gunk in older engines. This may cause some seals to leak slightly if they are in less than great condition (gunk may be bad, but it can help older seals do the sealing). But it's not all that common, and a regular dino oil with the same detergent additives will do the same thing to the same engine and seals.
Synthetic oil is not
really synthetic, as the word is defined in a dictionary. It is not created from elemental molecules, it is based on the same crude oil as regular oil, just very highly refined. Then the additive package is added (just like regular oil, and just like regular oil, what that additive package consists of is up to the company.... some are better than others) and you have the final product. Many 'regular' oils are almost as good as many synthetics. Synthetics start with an advantage due to extremely clean and pure base stock, but after that, the additive packages make or break an oil.
Switch away, eh.
