I prefer to decant wines, both young and old. It is a sign of respect for old wines and a sign of confidence in young wines.
Decanting old wines, just a few moments before they are served, helps to ensure that the wines’ clarity and brilliance are not obscured by any deposit that may have developed over time.
Decanting young wines several hours before they are served gives the wine a chance to bloom and attain a stage of development that normally requires years of aging. (thoughts on decanting by Christian Moueix)