Hi, GB,
Would this make sense?
You now make it clear that the gravestone does apply to Thorley(i) after all; and that 1858 was the year of his death.
Given that he was licensed in 1809, 31 years of subsequent service leads us to 1845, including at least 21 years (since 1824, according to Rees) as Master of a pilot-cutter. A proud family might very easily stretch this to "31 years as a master pilot": which would make your hunch as to 1845 retirement quite right.
As to the census, if he still owned shares in a pilot-cutter in 1851 (as well he might have done, even in his retirement) then there would be nothing greatly improper in omitting the word "retired" from the census form.
Fascinating!
v best,
BY