1643 is not impossible for a flintlock pistol, but statistically unlikely.
Ketler not listed in Stoeckel.
Lots of Adams. But none in 17th C. London, and only Alexander Adams in the flintlock era (Alexander Adams, London and Birmingham, ca. 1780-1810)
Please check your info! Best of all: get a good picture of the entire pistol, and the markings. Ketler may be a misreading.

Patrick