@Jack ***************
Correct, you need to be on the 5 year one first. In Australia, they allow IDPs to be issued on provisional licenses (at least the P2 licenses before the full one) while in America, you can get one on any license that isn't a learners permit.
Thailand is therefore more restrictive.
However, in many countries, there is no need for an IDP so a Thai D/L, even a 2 year one, on its own is enough. In neighboring countries, the ASEAN agreement takes precedence over an IDP so a Thai license is recognized, at least in Laos, Malaysia, Singapore, Brunei, Indonesia, the Philippines and Myanmar.
For Cambodia, it's fine to drive on a Thai license if you're driving a Thai plated car into the country but if you're driving a local Cambodian registration (such as if you're renting a vehicle there) you may be asked for an IDP. In Vietnam, they probably want an IDP if you can find somewhere to rent you a car at all.