Thread has gone a bit quiet, but I thought I would add my experience of FIRE.
I FIRE'd at 58, which is not that young, but I would still class as retiring early. I am now 61, and live off a DB pension and my investments (mainly dividend-paying shares and IT's, mainly in ISA's). However, I thought I would mention a few non-financial aspects of FIRE:
1. Get social. Unless you have a very active social life already, you will find you miss the day-to-day office banter with work colleagues. Go and find some clubs/organisations/voluntary groups to join for the social interaction. If they are during the working week, you will find you are amongst the youngest in these groups, so be prepared to interact socially with people 10 or 20 years older than yourself. I have joined a male voice choir, and have made many new friends from this.
2. Keep active. You should have more time, so use some of it to get fitter and healthier. I now walk to many places I used to drive to, and also cycle and swim. I have lost a fair amount of weight since retiring and feel much healthier than when I worked (which was basically a sedentary job in an office).
3. Be intellectually challenged. Keep your brain active, by taking part in something that stretches your mind. This might be further education, or some club with an intellectual challange - eg discussion groups. I joined a local discussion forum, and a medical research committee, from which I have learned a lot and kept my brain active.
4. Be worthwhile. Do something to maintain/gain self-esteem, which is all part of your overall personal well-being. Voluntary work is the obvious thing here - I volunteered for the local Air Ambulance charity as a speaker, which took me to all sorts of places, and made me feel I was still being useful to society.
5. See the world. If you can afford it, go and see the world, or the country, or your local region. Do it before you get too old. Start with long haul, as your horizons will reduce as you age. I have identified about 10 places I want to visit before I reach 70.
6. Stay solvent. The biggest thing approaching FIRE is to understand what you will spend, and therefore what income you will need. I under-estimated how much cheaper it is to live after FIRE, and have generally been too cautious in my spending. I hadn't quite realised how much tax, NI and work expenses were taking from my income when I worked. Also, after FIRE,you have more time to scrutinise what you spend, and I have found I have made very large savings in what I spend simply by finding bargains, changing bank accounts, switching energy suppliers and the like. I have been so successful, I am now struggling to spend up each month without generating new savings that I do not really need. The change in mindset from saving/investing as much as possible in achieving FIRE, to spending to enhance your quality of life has taken me some time to achieve.
Overall, enjoy FIRE - I do.