I'm not sure this is too unusual relative to our own society: these days life expectancy in Western countries is around 80-100, but people still tend to be considered to be getting old at fifty, relatively old by sixty and definitely old by seventy. In our case though we have the excuse that it's a recent change.

This implies pretty awful things about wizarding society, if we can safely assume that people with children retire around sixty and then spend the next century or so being ornamental, and that it's been like that for centuries.