There have been a couple such criminals in Canada in the last few years and IMO criminal profilers are having to revise their assumptions:
Col. Russell Williams, newly appointed commander of an air force base, long-time married, started stealing women's underwear at age 44 and in a couple years escalated to rape and then murdered twice before he was caught:
Col. Russell Williams: A serial killer like none police have seen
And then Bruce McArthur was caught for the sexual murders of 8 men, he had started his spree when he was almost 60.
McArthur is the oldest confirmed serial killer in Canadian history. His age may have helped him hide ‘in plain sight’
It does seem to be the person giving free reign to long suppressed urges and fantasies. Perhaps feeling confident they can get away with it?
At least this offender was caught right away.