The best works of Bach and Beethoven are from later in their life, although neither lived to be 85 (65 and 57, respectively), and also wrote great works in their younger years. Bruckner kept improving with age. There are also composers who lost it at a later age: Ravel, famously. Classical music is difficult, so experience does allow a better overall view, something which a lot of short works (such as pop songs) don't need.