Welcome to the OP. We have a bit in common. I owned a PC Insurance Agency from age 21 til I sold it at age 50. I poured my entire life into taking care of my clients and companies and it took a toll. I knew if I worked and saved/invested for 30 years I could FIRE. It worked as planned. It seems it worked for you too.
What I'd do differently ? Not much really. I sold my agency on a 10 year installment and the payments more than cover our living expenses. This allows our other investments to grow until we tap into them at age 61. We don't have half of your net worth, but we feel very financially secure. If I had it over again I would have pursued outside financing for the buyer and taken a cash deal. At first I worried a bit about the buyer's ability to make it work and make the payments, but he's done well and he's over 5 years into the 10 year installment plan.
I moved 350 miles from the small town where my business was located. When you own a business in a small town you can never really separate yourself from the business. I knew if I wanted my own life and identity I needed to change locations. It also helped the new owner establish himself as the owner.
Advice for someone your age? Don't over volunteer or commit to responsibilities. You will be approached by many worthwhile organizations, be careful with your time.
I have never had the desire to go back into a business. I know how hard it is to run a successful business of any kind and I'm not willing to sell my time again. Actually, since I ER'd I took over the management of all of my investments and rental property. If I add up the fees I would have been paying it comes to a great paying part time job.
Also, keep up with friends your own age. I was 50 when I completely retired and everyone my age is still working. I've lost contact with many of them. I ended up making friends with other retirees but they're 15 to 20 years older than me. They're very active and we do a lot of things that tire out people younger than us, that's good but I do miss socializing with people my own age.
I still get asked "what do you do" I found the best answer I can give is to tell them "I work from home" If they inquire further I tell them I owned a small business and am phasing out and can manage it from home. That is actually true, I just don't have to manage it very hard. I never tell them what industry I was in. The PC insurance industry is not a fun business that the public likes. Everyone has an insurance beef and I don't want to hear about it anymore.
Spend as much time as you can with your family. You won't get these years back. I spent too much of my children's youth in my office trying to please the public. DW was very patient, she was on board with the FIRE idea and I couldn't have done it without her.