Validation is a strong term used in many forms especially when it is being applied to an individual. From google the definition of validation is well explained by a "recognition or affirmation that a person or their feelings or opinions are valid or worthwhile." This form of the definition means a lot in our current society as many people face discrimination due to the lack of respect given to them from others.
An example of this can be seen in the LGBTQ community as identity is a key aspect to LGBTQ rights. This is on multiple spectrums from sexual identity to gender identity and cultural identity. One of the areas that is being worked on in particular is gender identity and pronouns. There is more than just two genders and that means there are more than two forms of pronouns. The most common are she/her, he/him and now a greater visibility has grown for the pronouns of they/them, ze/zir, hir/hirs. These other pronouns help to shine light on the different gender identities on the spectrum that include gender neutral, non-binary, and so many others. These are not valid terms unless people respect them though. Some people do not use these terms due to a lack of education or a refusal to use the person's terms. This is a true sign of invalidating someone's identity and reducing their identity, almost inhumanly.
Validation is also important in age as everyone faces discrimination because of their age at some point in their lives. This can be seen as someone not being seen as old enough or someone to old to take part. This discrimination comes from people making assumptions on people due to their physical appearance. So many times people have proved that age or perception of age does not reveal people's capabilities. Constantly people shatter expectations and defy what people thought they knew. So much more has to with ability, maturity and giving things a try. In truth your age may be a reason that you can or cannot do something but really there is so much more that goes into it. Validation comes from finding out from the person if their age is actually a factor or it was just assumed to be a factor. Validate someone by looking at it more on a personal level with multiple factors besides age.
Their is so many different forms that you can validate someone or invalidate someone. I find the biggest component breaks down into only a few parts, respect, listening to someone and not assuming information based on what your senses are telling you. Keep your mind open and validate others the way you would like to be valid to others. Spread the respect.