While you can never be sure how old it is, or more importantly how it was stored by the person you bought it from. Were there any clumps in it??? Could be an indication that it was stored where some sun got to it and it clumped.
With the cap on shake the hell out of it and make sure it's nice and loose. Are you dipping or using a fluid bed??? If dipping do you stir the powder after 2-3 jigs to keep it loose?? What are you using for your heat source?? I know it's alot of questions but the more we know how you use it the better we can help.
Last question?? Does it cure right?? If it does I wouldn't worry so much but you didn't say anything about that. Give a yell if you need more help