Can seniors in their 80's with limited mobility who love nature have a problem with the hike to the flume?

There is a shuttle bus that will take you from the visitor center close to Flume Gorge. But there is still uphill walking and stairs to get to/through the gorge itself.

Yes. There are a lot of steps and the path can get quite slippery if it's wet. There is a bus service that runs to the flume but to really see it you would need to go downstairs