Is it bad to take old medication?

Specifically mental health Medications, more specifically Seroquel XR (an Anti-Psychotic)?

I'm not planning on getting refills until I switch to new insurance as I don't want to spend thousands on medication just to be cut off from that insurance in March.

I'm not going to run out any time soon, but I'm wondering if it's bad to take old medication, by old I mean the oldest might be a couple years old, but I also have a lot that's only a few months old.

I'm trying to save my flex card money for 2 teeth implants (cost could be thousands of dollars each, and I'm about 6 months until done with braces which are costing me $6000 total)