You can be charged for five years because $320 is a 4th degree crime. But they likely will not if they have not but they could. If you pay the $150 civil demand they still can charge you but they likely will not. They may not charge you if you do not pay or they may either way. Read the AVVO archives for all the different opinions. You seem cavalier about theft.
Immediately consult a local criminal law attorney to discuss how best to handle this matter going forward - many offer free initial consultations
This is not intended to be legal advise or as legal representation. I am a California personal injury attorney . Be aware that every state has its own statute of limitations; and statutes & case laws that govern the handling of these matters.