You actually said, "Yeah - sorry. It was shorthand for the over 70 demographic where most Tory voters are found."
Most over 70s might vote Tory, that doesn't mean most Tory voters are over 70.
You say yourself that 20% of the population are over 65 so clearly less than 20% are over 70, it is more like 13%. There were approx 47.5 million people of voting age in the UK for the 2019 GE, the Tories got 14 m votes, if less than 13% are over 70 the absolute maximum Tory votes from over 70s if every one of them voted and they all voted Tory would have been 6.2 m votes so less than half of the 14m Tory votes. Of course they didn't all vote, people like my relative with dementia, and they didn't all vote Tory, like my DH, my siblings, their partners etc.
Clearly the Tories found most of their votes in the under 70s. Not surprising if 87% of voters are under 70. I wish we could get rid of this fallacy about the over 70s being responsible for the Tory win.
I googled the figures so can't swear to their accuracy but they seemed like reliable sources.