The minimum age to rent a car depends on the country and sometimes the state or rental company policies:

• In most of the US, the minimum age to rent a car is typically 21 years old. However, some states like New York and Michigan allow rentals from 18 years old.
• In the US, drivers under 25 usually pay an additional "young driver" surcharge.
• Some major rental companies like Hertz rent to drivers as young as 20 (18 in some states), Avis and Enterprise generally require renters to be 21 or older (18 in NY and Michigan), with young driver fees applying under 25.
• In Europe, the standard minimum age is often 21, but it can be as low as 18 in some countries like France, Portugal, and Germany.
• Some rental companies also require you to have held your driver's license for at least one year to rent at a young age.

So generally, you need to be at least 21 to rent a car without restrictions in most places, with limited exceptions allowing 18 years old rentals often accompanied by additional fees and vehicle restrictions.