Can an aloe plant "go bad"?

I am an officer in my school's Botany Club, and there's an aloe plant in our greenhouse. It's a fairly old plant, possibly up to 20 years old. Two years ago, the plant had no odor, and was filled with a tough, clear gel. Since then, it has gotten progressively smellier, to the point that it's causing people to gag when they smell it. Also, it's insides have steadily been turning yellower and runnier. Is the plant "going bad", and is there anything I can do to help it?