Wikipedia articles, as Joe Blow notes, have enough information to answer the question.
In addition to "hardship" licenses, there is a more common distinction between "restricted" or "provisional" licenses and full licenses. The limitations of provisional licenses vary by state; they typically comprise some combination of the following:
- restrictions against driving at night
- restrictions against carrying passengers, which may be based on the number of passengers or their age
- probationary rules that delay the acquisition of a full license if the driver commits any violations while holding the restricted license
According to the list, no US state offers a full license to drivers younger than 16 years old. The following states offer restricted licenses to younger drivers:
- 15 years, 6 months
- New Mexico
- South Carolina
- Wisconsin
- 15 years
- Idaho
- Kansas
- Montana
- North Dakota
- 14 years, 6 months
- South Dakota (reduced to 14 years, 3 months after completion of a driver's education course)
Source: https://en.wikipedia.org/wiki/Driver%27s_license_in_the_United_States
In addition to the US states noted above, the following jurisdictions permit drivers younger 16 years old to drive without supervision:
- El Salvador (15 years)
- Malaysia (15 years for "light vehicles" and "commercial vehicles")
- Sweden (15 years for "EPA-Traktors")
The Wikipedia page lists the minimum age in the Northern Mariana Islands as "15/16", but this appears to be a misreading of the cited source, which gives "15/6" (that is, 15 years, 6 months) as the minimum age for a learner's permit, and reports "no data" for other stages and restrictions of the jurisdiction's graduated licensing scheme.
Source: https://en.wikipedia.org/wiki/List_of_countries_by_minimum_driving_age