OSHA does not grant, nor empower others to grant, aerial lift certifications. It only requires that drivers be over 18 and have a verification of completion of training. This verification is sometimes referred to as an “aerial access card” carried by drivers, though in practice most OSHA enforcers access training records in an employer’s office.
Here’s what OSHA does require for aerial lift training, in its own words:
The employer shall have each employee who is involved in erecting, disassembling, moving, operating, repairing, maintaining, or inspecting a scaffold trained by a competent person to recognize any hazards associated with the work in question.
The word "certification" literally does not even appear in the aerial lift training standards guide put out by OSHA. You can see for yourself by clicking the above link and searching the page for "certification."
Not to put too fine a point on it, but anyone claiming to sell you an aerial lift “certification” is either ignorant of the rules (not a good sign), or is playing fast and loose, hoping their potential customers don’t know any better (very bad sign).