I know what you mean about getting older. I have a car that needs a fuel pump replaced. I have done a few in my time with great success but my nuckle skin is thinner and they bleed more. To add to that it seems like Murphy's Law comes into play more, complicating things. Then there are the time limits that a repair has to be made. It also takes longer to get up after getting under the car and the recovery from using musles that have not been used for a while. But the satisfaction of a job well done makes it all worthwhile, I think.