Our GSD is just past 11 years now. I get it. They are family.
Ours is slowing down. It's been coming on the past couple of years, but this summer seems more pronounced and advancing at an increasing pace. No incontinence issues like you describe, yet. Just achey bones. Arthritis is setting in and she is slowing down. Slow to get up. Less excitement about going outside. Debates about whether it is worth it to get up for things she used to be across the room for already.
I supplement her food with glucosamine with chondroitin and MSM. It seems to help a little. Although the benefits may be diminishing as she ages and progresses beyond what it can offer her. It's summer here (and humid and hot) and she doesn't tolerate the heat as well as she once did, though I would never consider shaving her. She's in the A/C most of the time, unless we venture outdoors to do yard work or something. Or someone is in the pool... then she *has* to be out there, too.
She does have orthopedic beds for sleeping. She doesn't always choose to lie on them, which is fine, the tile is cooler. But she is opting for them more often now than she used to.
I don't like to contemplate a year or two from now, but it is coming. :/
I don't have any suggestions for the bathroom issues, except check with your vet (get an exam) and see if there is a problem that you can address. A UTI or something. Beyond that, I would stick with comfort measures as best as you can. Perhaps the vet could suggest some dietary tricks that might help with it if it is purely age.
Blessings.
ETA:
Like Suz, our girl has been impossibly meticulous about doing her business outside. It's just unheard of for there to be an accident in the house. I posted several years ago about her having some seizures (she recovered and is on daily meds for thyroid and anti-seizure) and soiling inside was devastating for her. It only happened once (and while she was extremely ill, seizing) and she urinated a few times during recovery when the steroids made her drink excessively and need potty breaks every 100 minutes (not exaggerating). She was upset when that happened and we made every effort to prevent her from being in a situation where it might occur (I took her with me for anything requiring me to be gone from home more than an hour).
When the time comes that she has incontinence issues, it will dictate how we proceed to a great extent. Embarrassed is not quite the word for a good dog who goes in the house. It's defeating for them. I won't want to put her through that. Not looking forward to that decision when it eventually becomes an issue.
Perhaps your dog is not humiliated by it to the same degree. And that would make me deal with the inconvenience for a good bit longer. I suspect ours will become terribly depressed.