Is a 20 year old white wine all right to drink?

No, a 20 year old white wine is not an appropriate wine to drink. White wines are generally meant to be consumed within 2-3 years of their production, as they tend to lose their freshness and develop off flavors over time. Additionally, the quality of a wine starts declining after 10 years, no matter how well it has been stored. In some cases, they can even become unsafe to drink if the wrong storage conditions are met.