My knees and elbows are stiffer than they were 10 years ago. The knees usually take some work to get working 100% but I was a Paratrooper and Air Assault. So a lot of jumping and landing with heavy loads. A lot of running and walking through the woods with the same as well. My elbows honestly have to be worked evenly or I develop imbalances from the amount of tissue pulling one direction. Those hurt a lot... I have to superset all of my bicep and tricep work to prevent strain on the joint. My lifting is on a 3 day split as a result, otherwise I start having issues with my joints anytime I have to actually put a load on the muscles.
I have been on TRT so some of my imbalances may have resulted from responding extremely well to the Clomi and Test treatment.
For my back, I stick to back extensions and heavy deadlifts with heavy rows and lat pull downs. I do not trust myself to do pull ups because I have a fake clavicle and have nerve damage in my left arm. With the lat pull down I have no issues pulling heavy and just releasing the weight, if I were to lose my grip mid weighted pull up I would likely hurt myself.
Basically now, I do not rush myself for anything. I know if I needed to act in a hurry I can, but there is no reason to injure myself while not in an actual situation requiring that.. I run a GVT(like) program and just push myself as long as possible with a 3 week at 35% 1RM and 1 week 5-3-1 progressive week into a one week deload. So basically a 4 week on 1 week off work schedule. I have looked at those crossfitter people, and to me it seems that it works well for people that have never really been in any sort of shape in their life before, but I don't need it. I certainly do not need some asshat with a whistle chasing me around like I'm some sort of Private or something. I would likely want to shove the whistle through his teeth with my fist after the first hour. Not sure if any of those other programs are different than that, but that is what I saw while watching the Crossfit gym locally here. I have trained in the military fashion and for competitive sports most of my adult life. I have no problem designing my own program for myself. Once you understand how to see what your weaknesses are and can tell what is going on with your body by feel it's not hard to determine what sort of program you need.
I built muscle really easily, but I also get fat easily, so I have to have cardio mixed in and a lot of volume to keep that growing constant. If I stop lifting for more than a week it literally takes me two hours to get the blood flowing well enough to lift at my norm. I have a really slow metabolism normally.