Is it Possible to Train too Hard?
Sure…if you do 100 sets of biceps curls in a workout. Or 2000 pushups a day. Or run a marathon every 24 hours.
But for normal lifting routines, generally not…unless you are rest-pausing 15 sets to failure back to back.
For a typical lifting routine, you will get to failure long before you body breaks down, and the workout becomes counter-productive. Try a set of 20 heavy squats, or a day of German Volume Training with squats. That is about as hard as it gets, and it is wonderful for growth.
Also, it has been shown that workouts over an hour are catabolic. Get in, lift, and get out.