As far that I know but I am not sure, you may ask the recruiter for age waiver.
Anyway, if I were you I will be doing the following:
1- Continue maintain my self as a good resident until I become a Citizen. Avoiding crimes or breaking the law.
2- Continue looking for Linguist jobs that does not require Security Clearance, because Citizenship is requirement for any Security clearance. They are very few but I could find one if I continue looking such as Open Media Analysis. This job for example will need a linguist who monitors Arabic TVs and websites and write report about them in English
3- When I become US Citizen it will a lot easier for me to be cleared
Good Luck brother