An academic like that doesn't tend to retire, as they don't tend to be 'working' like the typical office plebe. He'd no doubt be making his own hours and effectively 'working' to satisfy his interests. Retiring is equivalent to stopping his passion.

My observation is that it tends to be the case with any industry-leading expert that they sort of transition into part-time work but pick and choose the work they do so that it isn't really 'work' to them. Holding that much clout has upsides.