There are no limits to anything you've mentioned, it seems more like you're just ready to give up on life?
Career changes can come at any time, the older you get, the more knowledge you have, and the easier it is to do something else unless you wasted your whole life playing video games. Look at the things you've learned through hobbies, surely something would apply to a job?
Why do you think a healthy love life would ever end? I've known many people who are great-grandparents, lost their partner, and met up with others who are in the same position. Now they have two huge families instead of one. If you can't get past thinking about sex, they make lubricants specifically for older people.
What do you mean by an active friend circle? Everyone changes their activities as the have a family and grow older. You adjust what you do as the body can't keep up. That doesn't mean you don't enjoy what you're doing, it just means you find new things that you enjoy. Hell some lady set a record for parachuting at the age of 104 last year, and the guy she took the record from got back out a couple weeks ago and set a new record (he's now 106). If you think you're ready to roll over and die in your 50's then you're not even trying.
Quite frankly I'm in my mid-50's. In the past year I actually decided to look at where I'm at for retirement because I intend to enjoy the hell out of it. Doing a little shuffling of my finances to try to boost some of my funds over the next 10-15 years, but otherwise I feel like I'm in good shape to kick back, do some traveling, and work on a bunch of projects. Retirement just means you get to start playing without work getting in the way. Even before then, I'm planning on building a trailer this Summer and cleaning up the motorcycle so I can get out and start riding again soon. There's no such thing as life being "over".