Is it fine to use reading glasses regardless of how much you need them or not?

Yes: Presbyopia is the loss of focusing in your eyes for near vision. It happens to everyone to some degree starting in your forties. Using readers simply helps to bring the focus back at a near point. You cannot "over-use" them and using them more will not make the eyes more weak. The loss of reading vision is progressive and will naturally get weaker into your 60-70's and then level off.