"If it doesn't CHALLENGE you - it doesn't CHANGE you".
Most people I see in gyms weight train without the intensity necessary for change.
If change is what you are trying for, you need to chose weights that will get you close to failure in a given range of repetitions. For example, if 10 is the number you are working with, you should not be able to do 15 repetitions with the weight you have chosen. At the same time however, working to failure would be too extreme and by that I mean dangerous.
Go for leaving a little in the tank but not so much that you lose the intensity. If you truly work hard enough and you have a plan, change should be attainable at any age.
