One of the things I was most surprised by when I got into the jobs business over a decade ago was the prevalence and practice of age discrimination in hiring right here in the USA. Oh, sure... we're not like some overseas markets where job ads explicitly demand youth, or a particular gender, or beauty(!), in the applicant, but there it is...
Besides presenting new opportunities in your job search, volunteer work can fill in the gaps on your resume, according to Stephen Van Vreede and Steve Burdan, both certified professional resume writers who work with TheLadders.
When it comes to presenting volunteer work in writing, treat it like a job. Certified professional resume writers advise clients to handle an extended volunteer job on your resume as you would any other position, provided it is related to your profession and you can demonstrate what you accomplished at the charity.
It should be listed in your job history, with all the relevant information, but the entry should clearly state that it was a volunteer position.