The Working Holiday Visa (subclass 417) is a temporary visa which allows people between the ages of 18 and 31 to live and work in Australia for up to one year. The second year visa is simply an extension of the first year visa, available up until the age of 31.
The Government is considering options for expanding the upper age of eligibility from 30 to 35 years. The current age of eligibility (18 to 30) still applies for the moment.
If you apply for the Second Year Visa in Australia, you must be in Australia when the visa is granted.
If you apply outside Australia, you must be outside Australia when the visa is granted.