The most important thing to understand when training athletes is the difference between G.P.P and S.P.P. Also, it's important to understand that mastery in a specific discipline does not mean mastery in weight training. In fact, it is usually the opposite; master of one thing, beginner of another. This is very lucky for you, whether you are a coach or an athlete. What this means is that you don't need advanced or fancy training methods to achieve results. Besides the huge pile of dung that is "sport specific training", the misunderstanding of training mastery by elite athletes is ruining training.
I know there are a lot of variables to this question but do you find that older lifters (over 55) respond better to full body training 2 days a week or focusing on one main lift a day 4 days a week?
It doesn't matter at all - for any lifter. People get so caught up in this stuff, and I totally understand why, but it doesn't matter at all. Just like where you put the bar when you squat, what kind of grip you take on chins/pull-ups, casein vs. whey...I should write an article on this. Just a lot of bickering and ridiculousness.
Anyway, with an older lifter there are a couple things that need to be addressed/looked at. First...