I'm not sure if this is a concern or not, but if you shake it, then put it in and want to use it immediately... I wouldn't. We were told some years ago that shaking this stuff could cause bubbles of various degrees and might send a bubble through your lines and to prevent any problems.... not to shake it right before putting it in. If you must shake it, do it like 24 or 48 hours in advance. However, if you gently roll it around in your hand, this will do the trick.
Same thing applies from the old days when using paint. You don't want to agitate this stuff to the point it has bubbles, especially things like clears and top coats. In fact they tell you specifically to never stir some of this stuff before using.
As for the age, I've used stuff that is over two years old without any hint of color shifts or problems.