In the hard man category, a cycling buddy of mine did 1.5 million feet in one year, but he was a kid of about 50. He originally set out to do 1 million, but found it too easy. OTOH he was raised in an igloo on the south slope of the Brooks Range. I'm not sure he could feel pain.
But back to the OP . . .I think 7,000' in a day is a totally reasonable goal. That's doable without being a good climber. You need even grades of ~4% and just keep pedaling. Up you go. It's going to help a lot if your BMI is not much over 25.
__________________
Results matter