I 'retired' at 50 - in fact, I won't start receiving a pension until 60, but had other sources of income, so could manage the bridging decade. I have loved it. I've studied, passed exams, volunteered, written a blog, read a lot more, acquired a dog, more DIY, cooking and gardening skills, been available to help my (now very old) parents with their challenges. It's been an unalloyed benefit in terms of health, weight, fitness, looks, money (I've learned to make our money go much further now I'm not spending to mitigate stress) and happiness.
I am an introvert, and I can manage with a very low level of social interaction outside a very small circle though. And I'm married to someone of similar bent. If that doesn't apply to you, you'd better be aware of it, and take steps to counteract possible loneliness.
I'm five years older than my DH, however, and I don't want to wait 13 years for him to retire, and spend my 'golden decade' sitting at home with the dog. So I am making sure we get our ducks in a row so that he can step back in the next 8 years and join me on more adventures. And I am looking forward to DS being wholly independent (still supporting him through university), so more of my income can go on language trips abroad and my other interests.