RocktheCasbah Yeah I think Hitchcock's own conclusion at the time was that Stewart was too old and that's why the film bombed (and it might be true), but I'm with you, I think the performance works BECAUSE he was getting on. There's a mental frailty to Scottie, steeped in regret, that a younger actor just can't carry. It's easy to imagine how the character's inability to come to terms with reality because he's in love with an idea doubled as Stewart's own struggles to accept that his leading man days were slipping away.
I think the other issue with Vertigo at the time probably was that it, unlike 99% of everything Hitchcock ever made, was "boring". Today we're looking back at it in fascination, like you study a painting or something (especially with that gorgeous technicolor), but it's probably not a coincidence that the very next movie Hitchcock made, North by Northwest, was the most thrilling in his filmography (ironically carried by Cary Grant who was even older than Stewart!).
Always loved the Swedish title for Vertigo by the way, which translated to "A study in red".