Many people are confused about warming up. Hollywood seems to think that you should stretch before lifting weights because thats what they always seem to show in the movies before they do their ten kazillion sets of bicep curls.
The goal of warming
The older you get, the longer it takes to warmup properly for heavy lifting. Warming up is about preparing your muscles and your joints for the heavy loads they are about to experience. The older you are, the longer it takes to warmup.
So to warmup for lifting weights, stretching doesnt help at all and cardio alone is not adequate - you gotta to warmup sets at 50%, 70% and 85% of your 8 rep weight. No need to warmup for every exercise, thats a waste of time.