Technically, most Ambulance Services do not set any particular age limit for applicants to become paramedics.
However, most Ambulance Services do require that their paramedics have a full un-provisional drivers licence before they can be employed. So, depending on the state, most employees must, at a minimum be 18 or 21 years old depending on their state age for obtaining a full drivers licence.
However, it should be noted that employment as a Paramedic is often very competitive and it is unlikely (but not impossible) for people to become paramedics without having other work experiences or tertiary qualifications.
If you’re keen to become a paramedic I wish you luck, its the best job in the world.