Have you narrowed down what aspect of diving that you want to be more senior friendly? You mention not being as flexible & finding it hard to keep up with younger divers. These hint at both above and below water aspects.
The posts above provide some good pointers, but you may want to narrow down the exact feature(s) you value most as being senior friendly. Is it the effort to get ready or the actual swim?
Below water is simple: stay away from "herded" dives where the young buck DM takes you on a marathon swim with all the other young divers. Note that this choice may limit the types of diving that you can do (maybe no more drifts?). We no longer use ops that enforce "stay with DM" guided dives.
For day boats, if a DM guide is available, we make sure to inform them before every dive that we are slow swimmers and we will fall behind. We tell them our maximum planned depth and indicate that we will check in with them as "catch up" to us on the return leg to the boat. We also tell them our planned dive duration (i.e. see you back on the boat in 60 minutes). We have never had any issues with this approach (since we knew ahead of time that staying with the DM was NOT mandatory).
Every live aboard we have been on allows us to dive our own plan. They do set limits (130 feet, 60 minutes, 500 psi) but your buddy pair are free to swim as slow and as little as you want.
Above water: limit schlepping of gear and effort to get to the site. A live aboard is excellent for this. Room to gear station to dive site is less than 100 feet. Very low effort. A live aboard also minimizes the gear set up effort as you leave your BCD on the tank all week. You also minimize the distance you carry your gear: about 20 feet. There are also many dive resorts that provide "front porch" diving that reduce this effort as well. On Bonaire, think Captain Dons, Buddy's & Divi Flamingo (and I am sure there are lots of others...). You can store your gear close to the dive entry off the dock. You can dive your own profile with your buddy and swim as little as you want as often as you want.
Every dive operation I have been with will help divers get their gear and themselves into and out of the water, so this seems less of a concern? This may limit shore diving that you do on your own with just your buddy.
My whole point is that there may be some specific issues that you can focus on and some others that maybe are not as important. This may help to point you in the proper direction for finding your version of senior friendly.