As this is the Australianised version, it's worth while noting that there are a number of Australians who have actually FIREd. I have organised and attended mustashian meetups in Melbourne, Canberra and Sydney. I have met about a dozen Australians who have achieved this, who I met on this forum, as well as knowing several people who retired early without reading any FIRE authors. There are also a number of Australians who haven't retired, but have met their number. Almost none of these people have ever worked in jobs that earned the sort of money that MMM earned, but they have done it.
Australia has a few challenges compared to the USA. Food tends to cost a bit more here, as do services, and petrol. We have a much more thinly scattered population, and we tend to pay people a living wage. The big challenge is, of course, housing. To just about any person from the USA, our housing costs are eye watering.
However, although the media make a lot of hype about our housing costs, and often run articles that say that no current 20-something can afford a house, I know a lot of young people in this age group who have managed to do so - without resorting to the bank of mum and dad. The young people I know who actually own property tend to be tradies, or people who have not done expensive degrees. But I do know several young people who started while they were in university, buying investment properties in smaller cities with diverse employment, and gradually working up.
These are options that FIREd people have also used. Everyone I can think of who I know who's FIREd chose an option for making their property investment easier. These include buying small investment units, furnishing them, and renting them furnished; getting a lease for a share house (while at university) and charging the other people in the share house enough that they weren't paying anything themselves; letting rooms in their house; buying a fixer-upper that was a lot cheaper than other homes in the area and gradually doing it up. The people who initially leased share houses, then went on to buy houses to be share houses (one had about seven before she finished her degree).
Because many items in an Australian budget are more expensive, a group of mustashians worked out several years ago that the $25kUS budget was probably equivalent to about $40kAUD. While this reduces the gap (available for saving) between an average Australian wage and the average US wage, FIRE in about 10 years (from them working out that it could be done) has been achieved by each of the FIREd people I'm talking about, and only a couple of them had high income. As it takes some of us a number of years to find out about FIRE, the actual age of FIRE has ranged from late 20s to about 60. It's also never too late to put together your own FIRE plan, and to put it into action.