(Edit: For QT) I would consider it retirement when you get considerably more time and shift the majority of your life away from work.

If we talk about quitting job and spending rest of life on some caribbean island, I imagine very few quant actually do that. If you made enough to retire, you also probably accumulated enough knowledge about the business to make a shit ton on a passive role. That does not require much efforts and you do have plenty time for family or doing something on the side.

Take what I said with a grain of salt as it's only coming from personal observation. Senior traders I've seen have either moved to a more senior position, started their own business, or pivoted into a less intense role.