Personally, I think the term "High Mileage" has changed radically as cars have progressed. I considered the 1984 Cavalier my family had to be "high mileage" when it reached about 100,000 miles.
.. the 1983 Ford Escort my parents owned was already at that marker around 60,000 miles.
Pretty much, anything built before about 2000 (give or take a couple years) was considered 'high mileage' category by about 100k miles.
I would say though, that some time after 2000, carmakers seem to have started making them better.. at least overall.. and thus they seem to last longer. Yes, some cars still won't really last longer than about 100k, but overall, I'd say newer cars just last longer.
.. I'd say most cars built from about 2005 on could easily make it to 200,000 miles with regular maintenance.. so "High mileage" on one of these would be starting between about 150,000 and 200,000 miles.
My 2010 Fusion has already hit 210,000 miles, and I'd say is still in great shape. I think it's fair to call it a 'high mileage' vehicle, but honestly, I see no reason that it won't make it to at least 350,000 miles reliably.