It was 16 but only with parental consent and only with a marriage partner 21 or younger.
16 with parental consent is quite common. Mississippi I think is 15. Some allow marriage younger than this (some have effectively no minimum age), but with the requirement for consent to also be sought through the courts.
I don't know how they do it in the US, but in the UK most big companies outsource application checks to several big clearing houses. They handle the logistics of checking qualifications and obtaining references from previous employers, plus the optional enhanced checking that some companies need (such as DBS/criminal record checks).
In the UK there is a single official centralised system for checking degree qualifications which covers most major universities. It's also only a 5 minute job to email a university registrar directly. I think most big companies would consider this a bare minimum task when recruiting for any role where a qualification is in any way important.