As violins age, the wood becomes more resonant and produces a warmer, richer tone. The varnish used on older violins also contributes to their superior sound quality, as it hardens and becomes more elastic over time, allowing the wood to vibrate more freely.
In addition, older violins have often been played by many musicians over the years, which can further enhance their sound. The combination of these factors contributes to the belief that older violins produce a sweeter, more desirable sound than newer ones.