Hi Mary
I think that depends on when he started writing and when he stopped.
If he wrote his first book when he was 20 - and it's unlikely he'd start any earlier - and continued writing until he was 65 (when he was issued with his free cart pass and decided he's said all he had to say) he would cover 33 years in the 18th century and 32 years in the 19th century. Aaargh, I've made this difficult - even stevens so far.
However, he may not have been at the height of his writing powers until he was 40. But his writing style may have become entrenched in the 17th century.
Of course he may not have started writing until he was 45 and carried on until he died.
Short answer is: I don't know. Or 'he's both'. Neither very helpful.
If you're talking about a real writer, go by accepted wisdom, I guess.
If you've made him up, it's up to you.