Thanks for writing. You have reason to be concerned - and I'm glad you turned to JA as your first step. I'm also glad to see that your son has agreed to consider counseling.
There could be any number of diagnostic categories that might fit your son's behavior/feelings (the way you described it). It is inappropriate (and unethical) to diagnose over the internet (through a third party and across the ocean)... but there could be a host of issues that might explain his behavior. These issues could range from simple adjustment-to-life issues to more serious concerns like substance abuse or even frank mental disorders.
I would urge you to consider working with a Licensed Mental Health Professional (LMHP) to begin this process. The first step is an indepth diagnostic work-up - which is often done through clinical interviews and perhaps even some specific diagnostic protocols. Once a diagnostic profile is completed, appropriate treatment can be developed and implemented.
While "anger management" classes may certainly be helpful - and recommended following the diagnostic work-up - if there are more serious concerns, just treating the symptom (anger management) won't make the problem go away. Among the LMHPs I might consider - I would likely begin with a Clinical Psychologist... but this likely reflects my bias as one. Psychiatrists and Social Workers may also provide such services - but they sometimes don't have access to the same in-depth diagnostic protocols available to psychologists.
I wish you and your son the best of luck. Thanks for writing!