My dad has never been bowhunting and wants to give it a try this year. Luckily for him a friend of his is going to let him borrow his bow free of charge. The bow is an old Buckmasters Generation 2. When my dads friend dropped the bow off today his friend told him that he needed to get new strings because they where 11 years old. from what i can tell there is no fraying or separating of the strings my. So my questions is do i need to replace the strings since they are so old and the bow hasn't been shot in 4-5 years or should they be ok?

I would say yes. Most of the time the problem will be under the servings where it cannot be seen.

Besides something obvious, how would one know when it is time to restring a bow?

How much you shoot. A tournament shooter will change strings yearly, sometimes twice a year. If you put less that 500 shots on your bow a year, every 3 to 4 years if the string stays in good shape. If you string is several years old and your peep starts going haywire, get them changed. Something is letting go. If your bow loses poundage after several years and the cam(s) suddenly get out of time, something is letting go on the a cable. When inspecting your strings and cables, always check the end loops where they attach to the cam(s). Sometimes they will break.