Mine went at 240,000 ish, 07 V6. Right after a several thousand mile road trip.
Which brings me to my next point, that alternator was on my mind for at least the last 75K miles but I thought it was cool to push it. See how long it would go.
This road trip included 100's of miles with no cell, no gas, no towns so if it had failed it would've been bad. The other vehicle on the trip (05 Tahoe) actually had the alternator fail but luckily we were already in Moab. Mine failed 2 weeks later at home which is a crazy coincidence.
My long winded point is yeah this isn't a service interval part but is it really worth pushing it? If my family had been with me and it did fail I can't imagine the drama with no cell signal in BFE.
Your mileage may vary