Isn't it normal for sight to deteriorate as you grow older?
No. The loss of focusing ability in later life is mainly due to acquired habits of strain and can be both prevented and reversed. Many quite elderly people have regained good near vision and more flexible focus after many years of depending on glasses to read.
Most cases of poor near vision that arise around the age of 40, if caught early, can be easily turned around, but often students going through this experience are surprised that the poor habits that led to the deterioration began many years earlier - sometimes as early as childhood.The first patient that I cured of presbyopia was myself.