I had to have an ECG for my FAA C2 and I am definitely not 50 yet
The figure is 40 or 45, I think.
I doubt the UN-qualified FAA Class 3 is non-ICAO but since so many people seem to think it is (yet nobody has yet provided a reference to this very simple and specific question) it's probably a good policy for a pilot flying an N reg'd aircraft to get the C2 medical if possible. It costs hardly more than the C3 and is likely to be half the price of the CAA equivalent for which I usually pay about £150.