For most of us, the shape of our eyes stops changing some time in our 20s much like our body stops growing. That then begs the obvious question: why does my glasses prescription change or why do I go from not needing glasses to needing glasses as I age?
As our eye ages, from a 20 year old to 30, 40, 50 and 60 year old eye, a number of changes occur which affect the overall "vision power" of the eye. Firstly the zooming lens loses its range progressively. The pupil size also shrinks with age. The density of retinal receptors also reduces gradually which is like losing megapixels in your camera
So for example, let's say you have an overall rugby ball shaped eye as opposed to a soccer ball shaped one. This should mean you have something called astigmatism which is the second number usually in your glasses prescription. A person below the age of 25 might have one point of astigmatism based on the shape of their eyes but not actually need glasses. Then as you age and those parts of your eye I mentioned change, the astigmatism appears to “come out" and affect your vision. But it was always there- it just didn't affect you yet.
That's why overall it is so important to look after yourself even when young. Because very few things get better as you get older, most things get worse and some health problems appear which you didn't even know about.