def returnSlotNumbers(parking_lot, driver_age=0):
    """Returns all the slot 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 

    slot_numbers = []

    for i in range(1, len(parking_lot) + 1):

        if 'driverAge' in parking_lot[i]:
            if parking_lot[i]['driverAge'] == driver_age:
                slot_numbers.append(i)

    return slot_numbers if slot_numbers else 0