Almost one-third of Americans say they’ll need to work into their 80s because they can’t afford to retire earlier, according to a recent Harris Institute survey. But in light of the difficulty even younger professionals face to find work, how will large numbers of older professionals — who are vulnerable to age discrimination, unspoken though it may be — be able to land new jobs, promotions or change sectors, if they must? Even if you’re well into your late 50s or 60s, don’t be defeatist: I have, over the years, seen many professionals from this age group land new and…