Age is just a mindset, in fact, it is a mental construct.
Now is the only real moment of our lives and always will be. All the time, another mental construct, that has come before no longer exists, it is just a memory in our mind.
Just live each moment and then your age is no longer dominating your self-image, your story of the past no longer influences you now and there is no need to worry about how many years you might have left and so on. You do not have to then think about acting an age!
Life, even on your death bed will always be now not what age you are on your birthday.