The only hill at Rose Island is the paved walkway down to the bridge. It is very steep.
I recommend you use the tour van. The tours are an exceptional way to learn about Rose Island and to see it first-hand. I myself had trouble coming up that hill, it's a 75% upgrade, extremely steep. My legs burned and were mush at the top. I have never walked a more challenging hill so far.
We're a bit younger than you but not by much. We ride our bikes ten miles every day and coming back up that hill was a huff. Remember you will have walked down the hill then around the interpretive trail and then finally back up.
I agree with Lynn Wagner. The paved path has one steep hill on it. It's not too bad going down it to Rose Island. Coming back up is the hard part. There is 1 spot that has a bench and a picnic table. But, it's closer to the bottom of the hill.
The tour of Rose Island is really good. They have a van that will take you to and from the beginning of the tour, so you don't have to worry about the hill. The only thing is that there is a lot of standing. We had several people on our tour that had to leave and sit down on a picnic table because of the standing.
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