My ski buddy is over 70. He doesn't have Indy. He got the senior discount at Brundage, which is for 65+. Saves $20 to get a ticket online in advance. But the software is fiddly when setting up a new account. He tried to buy a ticket using his phone and the Brundage WiFi while standing in front of the ticket desk . . . and gave up. He has more money than patience.
Using the Indy Pass with the card was simple. I handed over the card, and got an RFID card all ready to go. No charge for a plastic RFID card that is re-loadable. Turned out the first person I dealt with was from North Carolina. He and his girlfriend are young adults having a good time working seasonally out west, started with a few years in Montana and this winter at Brundage.
Bogus Basin is also 70+ for senior rates. Tamarack is 65+.