If you made a valid Will many years ago then its age will not automatically make it invalid. Even if you have lost the Will as you stored the original at home, or you accidentally destroyed your Will, or you cannot recall where it is your Will remains valid.
However, if you have married or formed a civil partnership since you made your Will then it will no longer be valid. It is best to review your Will every 5 years or when there are significant changes in your life such as buying property, having children or grandchildren, or because of the death of your partner, children, or beneficiaries.
By having an up to date Will you will ensure that your current wishes are reflected.