The Tories did best amongst the over 65s and turnout was, as usual, highest in that group.
The British Election Study doesn't indicate that the oldest voters turned out less in 2019 than in recent elections.
https://www.britishelectionstudy.com/bes-findings/age-and-voting-behaviour-at-the-2019-general-election/
Over 75s turnout was lower in 2019 than it was in 2017, but around the same as it was in 2015 which was held in May. They actually suggest the season as a possible explanation why over 60s as a whole voted less in 2019 than 2017, but that doesn't address why the winter effect would be more pronounced in the younger elderly but not the very oldest. Nor why the oldest voters would turn out at the same levels in May 2015 and December 2019.
I know people did worry at the time, but it's just not a very strong reason. Especially not for a group of people who will mostly know or suspect that the electorate will be serving them their P45s, and will have every incentive to drag their terms out.