Replacing bag gloves

I've got a pair of Ringside Super Bag Gloves that I've had for about three years. Use them once a week, every week, on pads and heavy bag. They aren't misshapen and padding doesn't seem to have shifted or anything like that.

In the interest of protecting my aging and troublesome joints (shoulder especially), should I replace them even though they look and feel OK?

Last time I was complaining to my doctor about shoulder trouble, he suggested I might try replacing the gloves. That was kind of a shot in the dark on his part, though, as he doesn't know anything about boxing.