Steel road bikes can last indefinitely if they are cared for (not allowed to rust). My oldest bike just turned 25 years old three days ago. Steel can also be repaired easily if it gets bent. Aluminum does fatigue and break (you will never find springs of any kind made out of aluminum) so you cannot rebend it back to the original shape if it gets bent without risking frame failure, and you can't change the spacing of your rear triangle for the same reason. I have 9 bikes. 6 are steel, 2 are aluminum, and 1 is carbon fiber/aluminum. Steel is definitely more comfortable than aluminum, especially for long rides like centuries and double centuries.