Why do my fluorescent lights flicker and require cycling the switch to turn on?
One of the bulbs also has one black end if that means anything.


That means it is an old fluorescent tube approaching the end of its life. Generally the end gets darker and darker over time. This is an effect of the starting process eroding the filament at one end.


  Do these low-medium end fixtures tend to wear out after 15 years?


No, they can keep going for much longer but some (many) will fail early and a few will last unexpectedly long.

Older installations used a starter that is worth replacing if you have problems.

I would test the tubes in another fitting that is working well (note: you can probably buy a cheap fitting for $10 and just use that for testing tubes)