How often should i replace my custom orthotics? as often as my running shoes? i feel like they aren't doing their job as well as used to.

Depends: A functional orthotic shell should last 5-10 years or longer. However, if there were certain modifications made to the shell, or there was a topcover (the soft part on top), those parts can wear out more quickly. Fortunately, most of the time these can components be rehabbed rather than just getting new ones every year.

Have them checked: See the doc who made them to evaluate them, they may need to be adjusted so they support your feet better. Good custom orthotics should last for years.

When symptomatic: Custom devices have a prescription built into them to help control biomechanical pathology. Over time, your biomechanics may change enough that your prescription may need to be updated. Average replacement is 4-5 years, with some people going 20+ with the same devices. If you are having pain, that is no longer controlled with using your orthotics, you should have a re-evaluation done.

No: I think that is too often. At 23 years old, i would imagine your feet aren't growing anymore. You are replacing sneakers becuase they are wearing out. Orthotics if custom made should not have to be replaced that often. Worse case scenerion if you wear away the top cover, you can have the orthotic "refurbished" where the top cover gets replaced. This is a lot cheaper then getting a whole new device.

It varies: According to the rigidity/flexibility of the orthotics, your size and activity level. Flexible orthotics may last only 2-3 years where some that are more rigid can last 6-8 years or more, with only some minor refurbishing as mentioned above.