Curious if it's this black and white. Normally, younger people are advised to have portfolios that tend riskier, as they have more time to make up for downturns in the markets, which (it is at least taken for granted) otherwise are on a perpetual upward trend. Even if we assume retirement still happens at 65, and you're just extending the length of retirement, that'd be a reason why you need your portfolio to do MORE heavy lifting for you to get the amount you'll need to cover that long retirement, so it'd suggest a higher appetite for risk. If you're working longer, on the other hand, all the more ability to weather downturns in the market, and so less out of necessity and more opportunity, the appetite for risk would also seem to increase, for most persons.
I assume you were talking more about physical risk taking though, because as "tomorrow you may die" becomes less and less likely, you're perhaps that much less incentivized to "live for today" (to deconstruct the popular boomer adage). This angle I'd take less issue with.