There's always instances of small amounts of fraud, and probably some hijinks in some counties by election officials, but for the whole election to be null, it would have required a lot of Republican...
Think they thought if they used more force it would have escalated things to a dangerous degree, with the president you know, egging on people and stuff.
I'm about 45 years old. Upper body strength is just as good as I was younger. However, I do get tired more easily. One thing that definitely helps is falling into a routine.