def returnVRNsForDriver(parking_lot, driver_age):
    """Returns all Vehicle Registration numbers for all drivers of a particular age"""

    if not isinstance(driver_age, int) or driver_age < 18:
        print("Driver Age Should be atleast 18")
        return -1

    vrn_list = []

    for i in range(1, len(parking_lot) + 1):
        if 'VRN' in parking_lot[i]:
            if parking_lot[i]['driverAge'] == driver_age:
                vrn_list.append(parking_lot[i]['VRN'])

    return vrn_list if vrn_list else -2