Was that Croatia trip GCT or OAT. There is a difference in how strenuous the trips are. I, for one, am not fit enough to make the effort for an OAT trip. But I do manage the GCT trips, although I sometimes opt out of something with a lot of stairs. There have been people using canes or, occasionally, walkers (but those not all the time). Sometimes, I use a cane but only when the surface is very rough and I need it to give me confidence, not for support.
When I went to Malta when it was the base trip (2005 or 2006), there were two sisters traveling in the group who were both in their 80s. Walked with canes and moved slowly. My friend used a cane (later had a hip replacement), and I used one for what turned out to be only bursitis. One couple traveling with a single friend constantly complained about the pace of the trip. We had to wait here, had to walk slowly there, etc. Actually said, so that everyone could hear, that they didn't know why GCT accepted travelers who needed canes. In Mdina, we were waiting to get into something and, while we were, people began to arrive to attend a wedding ceremony in the cathedral. The rest of us were fascinated seeing the aristocracy arriving in limos or walking in, in all their finery. These people complained. When I wrote my evaluation, I mentioned their attitude and suggested that GCT take their comments with a whole salt shaker.
So if you are concerned that you might be sent home because you couldn't keep up, any GCT PD would not be quick to do that. Living in the Boston area, I have direct contact with some of the staff and I have been told that I'm correct in believing OAT is not for me. Not so, for GCT.