There is a well-known adage that says 'write what you know' and also one that declares 'everyone has a book in them'. These two pieces of advice would appear to be more poignant the older one gets, surely suggesting one is never too old to write.
Age brings with it many wonderful things. One has accumulated vast experience, defined one's standpoint on many subjects and begun to piece together the things that matter in life. Most of us will have had our hearts broken at least once, faced the death of a pet or person we held dear and have tried a few different jobs along the way. Relationships change and evolve as we get older, we may begin to see the logic behind the way we were brought up that seemed unfathomable to us before, or that in retrospect a lover was really not any good for us. Sometimes we can come to forgive people who did us wrong, having been through the fabulous gift of time's healing powers.
However, it is not only this life experience that can lend a richer depth to one's writing. If someone has been writing for a while, in most cases the kinks in their writing style will have been smoothed out too. Agatha Christie and Catherine Cookson are just two writers who came into their peak past their thirties, and carried on writing into their eighties and nineties, respectively. Although there may be an argument that people do hit a 'prime' in their writing life, past which their work becomes less inspired or more obviously formulaic, this happens at different times for different writers. There is also much evidence to suggest that people past this 'prime' still produce worthy literature that fans love, and is still superior to another writer of the same genre. If one does not start writing until later in life, it is logical that their prime will be later too - the age of starting should not be a barrier to striving for their best work.
If one only finds that the lure of writing haunts them when they become a new mother or father, say, this does not exclude them from becoming successful or prolific. Children will keep them up at night, fall ill, grow and go to nursery and school; thus a parent may be awake or at a loose end at odd moments of the day and many strange and wonderful ideas may happen upon them at these times. If he or she has a pen and paper handy, these can lead to great things. J K Rowling is the obvious example here.
At the other end of the parenting spectrum, there is the 'empty nester' with lots of time on their hands. Although we mainly think of mothers in this category, I am sure men feel the emptiness at home too and the void that may leave in their evenings and weekends. Maybe the new or neglected hobby of writing will be welcomed now, with new emotions and cherished memories to put on the page; or a fevered exploration of who they are now that they have let their offspring out into the world and do not have the same role as before.
Then, of course, there is the retired person with a new-found freedom and a licence to finally follow their dreams. Many people who retire pursue a creative outlet more, and even join classes and courses to indulge what were just hobbies before. Sixty-odd years of people and places and thoughts and theories may be ready to explode into life before them. Many people have been busy driving on high-powered and exciting lives and have never really taken the time to contemplate 'what it all means'. As soon as they slow down in retirement, there is a need to make sense of it all and/or relay to others how their lives have been spent. Great novels and memoirs may pour forth from this soul-searching. Something of themselves can be left to enchant future generations, and intellectual challenges of structure and story-telling can be met.
Of course, there are many other reasons why people choose to write later in life, but it is clear that no matter how old one is there is wisdom and energy that can be imparted. As long as one wants to write, I believe there should be no age barrier to telling one's story or conjuring fiction to leave for our successors. Even if it should never be published, our writing is a unique insight into how we lived and what we thought, and that should never be censored by age discrimination.