Yup, all that has been said. Several people in our club with movement disorders, injuries or just accumulations from old age. First times, until people know you, feel free to say what you are and are not able to do, but mostly no one cares. If you walk (hobble? limp? : ) through the COF the kids are running through, no one will tell you to hurry up.
Also, most kneeling and all (?) prone is prohibited, generally very little anymore. Even when common, club matches at least would generally not mind or have an alternative method to shoot without that, OR find a way to help; even in the old days you rarely got UP from low positions, so would unload kneeling etc. then could get help to get up.
Seated starts are a thing. If that's hard, think about how to do it safely, or tell them you can't. Most clubs are nice, won't penalize or anything but help.