The Transmission Temperature warning light is for when the transmission overheats, heat is a killer for transmission fluid and transmissions, once you have overheated to the point of the light coming on you have killed most all the proprieties of the fluid and could also have done some damage to the transmission.
Think about it all oils have certain properties that make them do the job of the lubrication, cleaning and or hydraulics that they are designed for, and after a time/use period loses much of those properties and also get contaminated, there's no such thing as "lifetime" fluid no matter what a manufacturer says, their definition of "lifetime" is their warranty period in which they are libel for fixing the vehicle, when they are no longer libel for any damage to the vehicle the "lifetime" has no more meaning to them, nor should it to you.
That all being said wouldn't you rather act proactively and change any oil/fluids before damage is done or wait in a light to tells you something no good has happened.
The only warning light that is good is the "Maint" light telling you it's time to change the engine oil, there's no such lights for when it's time to change the transmission fluid, coolant, or brake fluid, any light related to any of these are BAD lights, so it's up to you to decide when it's time to have "new" fluids instead of fluid that has lost it's properties, contaminated or both, I personally would rather have new fluids that I know are doing their job instead of fluids that are questionable if they can still do their job.
IMHO 180,000 miles is WAY past time to change any or all fluids.