Age on flintlocks is relative, flintlocks didn't become obsolete till the 1840's. As the weapon is clearly a high-priced hunting weapon the good condition isn't surprising either. This was a gun for the gentleman to go hunting with on occasion, not something carried day-in day-out by a pioneer on the frontier. To me the most surprising thing is that it stayed flintlock, most of these would have been adapted to percussion cap due to the faster ignition on the hunt. But then, if you had the money to buy something like that you probably had the money to buy a "modern" gun when percussion caps became available.
F 135 - the right choice