With age, champagne changes both in flavor and texture.
In young champagnes you often find impressions of citrus, white and yellow fruit, apple acidity, spring blossom, bread dough and brioche. Older champagnes have something else to offer.
Aging in cellar, on lees, and after degorgement in bottle, lowers the acidity in champagne and changes the flavor: in time you may smell and taste dried fruit, nuts, raisin, dried flowers, mushroom and forest aromas.
In addition to this the mousse, the bubbles in the wine, changes too: it becomes softer and gentler. In time the bubbles may even disappear altogether. What's left is an aged, still wine.