I don't really have any books on the subject. There was one that I came across from Human Kinetics called "Functional Fitness for Older Adults" by Patricia Brill. I have it. It is okay. It has some good ideas.
I saw John Graham give a lecture about some of the testing procedures he uses for his older clients that I was able to take a lot from that also.
I mean really, you have to look at the person, evaluate where they are at and know what the need.
Some people are in different places, even though their ages are the same. I mean, I had one guy that was 66yrs old and he was an animal. We worked up to a 200lb back squat, he did quick feet drills and low level box jumps. He was in amazing shape! then, I'll have people that are 50 and complete train wrecks.
There are a few things that I find very important for older clients though:
1) Most of them are extremely week posteriorly. I usually have a higher ratio of pulling movement to pushing movements. Most of their postures are very anterior.
2) they usually have weak calve muscles (hence the reason they shuffle around) so I train their plantar flexors as well as their dorsiflexors.
3) as evident by research (some that I posted, some from the text), the older we get, the more we loose the ability to recruit motor units. So, i like to do some sort of reactive training if I can. This doesn't mean, 42" depth jumps, but, it can be as simple as medicine ball chest passes. just getting them to move quicker can sometimes really make a world of difference, as well as help give them confidence when they are out in the real world. If they are able to bend down, I usually have them throw a chest pass to me and then I'll roll the ball back to them (either center, right or left) and have them react and get the ball.
4) teaching them to stand up is a really important thing. getting those glutes working. Not everyone needs to have a bar on their back. Just squatting down to a chair or bench and learning to stand up can be a work out in and of itself. they can hold DBs or a med. ball for that if they are able to do it properly. One of the tests John Graham used was the get up and go test, where the client sits in a chair, on the go signal, they stand up and walk 10ft. around a cone, and back and sit. That is a timed test.
5) grip. i find that older people usually start to loose grip, so working that with some light grippers can be very helpful.
really, I just look at where they are at, and where they need to be and then i think of things that can help them get better at living everyday.
The most important thing you can do is improve the persons quality of life. Like the 66yr old guy i talked about above. I mean, his main goal was to come in the gym and get huge! he wanted to be this big bodybuilder looking guy. Now, you and i know, at 66, that pretty much is not happening. So, I humored him a little and let him do some bench pressing, and I taught him how to squat and deadlift with good form and he got a kick out of it, and then I gave him the things he needed. In the end, the thing he was most happy with was that he was able to go outside and play soccer with his friends grandchildren, while his friends could only sit there because they had no ability to move or keep up! After that, he really understood what I was trying to do for him.
Hope some of those suggestions help.