Have you ever seen someone who worked sitting down all their life stop working? A retired mechanic becomes a tree-shade mechanic. A retired plumber consults with the company he built. A retired claims adjuster watches TV.
Most old people need something to keep them busy, or they deteriorate, fast. Part-time work sounds like an excellent idea for most. Again, they're retired, so they get to be damn picky about where they work and for what cause. If they're smart, this isn't wage slavery, this is choosing to work to keep your mind sound and feel a sense of accomplishment that you're used to.
Besides which, 65 is too low a retirement age considering how long people are living. If people were financially independent, it wouldn't matter, but since they're drawing on government money, it just gets way too expensive. It makes sense to bump that up slowly over the next couple decades.