The best way to tell a Gilbert clocks age is to inspect the back of it. You should see a label displaying the name of the company. Because this company changed its name various times throughout its duration, the name engraved on the back will help you identify the time period it was constructed in.

Why wont my pendulum keep swinging?

Have you recently moved your clock? The reason a clock pendulum often stops swinging, after being moved, is because the clock case now leans at a slightly different angle then it did at its former location. Dont worry about making your clock absolutely level with the floor and dont use a level.