We took my in laws at Christmas and both in mid 70s. Be flexible with your itenary. My MIL did fine mostly. FIL had more mobility issues. Hopefully boat has a "Gate" in lifelines to make boarding easier at dock. Can assess dingy transfers when there, but can have a ball without ever leaving boat , or going ashore only at marinas. Leverick, Scrub Island (Email before to confirm TTOL discount), Harris's Place on JVD, Soper's Hole, and others all make this pretty easy.

Find "their spot" on boat and assist them to and from while underway. Good luck!