No frame material is more durable than steel. It can ding, scratch, dent, even bend, and retain structural integrity. When well made and cared for, steel will last a lifetime.
The same isn't true for aluminum. Aluminum is more brittle, so it's more susceptible to failure through fatigue or damage. A single dent in the wrong place could render an aluminum frame unsafe to ride. And when aluminum fails, it fails catastrophically.
Think about it like this: glass will break before it bends. The same is true in many respects of aluminum. Steel on the other hand, will bend before it breaks, resulting in a far more resilient frame.
If OP wants a bike for life, he bought the wrong material, carbon suffers much the same issues as aluminium.