At what temperature do you blanket your older horse - When he tells me he is cold.
I let him grow his winter coat, I provide him with shelter if he chooses to use it (stall attached to paddock), and pretty much all the grass hay he wants (though he tends to get fat so I have to limit it some, but on the really cold nights (single digits or below) it is for sure free choice).
Some days I find him coated with icicles hanging from his thick winter coat while he is standing out in the weather, choosing to eat from the round bale.
Every now and again I find him cold. I add a water proof sheet to protect from the wind and he is good to go.
I am not anti blanket. I have one horse trace clipped and blanketed. I just prefer to let him take care of him being warm. So far his body seems to do a fine job of that.