If you are short-sighted (myopic) you will be wishing increasingly to remove your glasses for reading. If you have not previously worn spectacles it may be time to consider spectacles for near, maybe ready readers. Either way do not neglect to come for an eye examination as it is about this time that other conditions such as glaucoma may begin to become apparent.
The reason for the change is lack of accommodation, that is that the lens behind your iris is becoming less flexible. In fact it is a process which started in your teens, since which time your near point of clear vision has been going away from you whilst you see well in the distance. The effort of sustaining maximum output of the ciliary muscle can cause eyes to tire in your mid forties, and eventually you will find that your vision is no longer clear enough without some help. At this point you have a range of options from using simple single vision lenses, varifocals, bifocals or contact lenses.