When you sell doesn't really matter. The current value of your bonds (e.g.) will still drop if interest rates go up.

If you bought that 30 year at 14.5% and we had hyperinflation then you wouldn't be so happy. There was a reason why those rates were at that point, inflation was >10%.

Conversely you could try to short bonds now but if rates stay at zero for the next few decades or go negatively that's not gonna be so great. In the rear-view mirror someone will say how we were stupid(?) for not shorting bonds when the rates shoot up to >10% again, or they don't. It's hard to win this game.

What is true is that retirees might have a shorter horizon (though people keep living for longer and longer) and so they may be forced into safer/shorter duration investments and possibly into smaller returns.

Efficient markets something something ;)

While this is true for an individual investor, a large part of the market for fixed income investments is large investors who are liability matching in one way or another: either against a portfolio of life insurance policies or against defined benefit pensions. They genuinely don't mind if the value of their bonds falls due to rates movements because (if they have done their jobs right) the value of their liability stream will also fall by a corresponding amount.

Of course, you can then apply your argument to people who have pensions or life policies I suppose but those aren't things people often "sell".