Masters in US implies the OP has a past history of completing non-trivial projects. Built career is just a narrative that HR and investors like. Humans can learn quite fast lots of useful things. This is not a statement "everyone can become world champion" but rather, you don't need to become world champion to find contentment and happiness in life. Growth mentality is the key.
This sounds like glass half-empty type of view. While pessimists never get disappointed, it also skews ones perception of the world so that one does not see the inherent opportunities, nor does one act to embrace those opportunities. It's much better to ask "what is the best version of events" that could come out of this and try to act so that happens (even thought that will then lead to disappointments)
People can start and find wonderful and fulfilling lives in their 40's. Personally I have no idea what the OP is like and if this discussion is the only interaction you've had with the person, neither likely do you. Which means both of us are unable to guess what he can still achieve in life. A borderline depressed person will describe their circumstances and capabilities in a way that plausibly does not in fact reflect their full potential.
There are some career paths for which not only doors close at an early age but they require specific circumstances to even be feasible - like an Olympic gold medalist. Most lives are not like that (than heavens) and people are able to find meaning and fulfillment in lots of circumstances.
If you don't know a person, then the charitable interpretation is to trust they are capable of humanly achieving what ever they set their minds to, that people starting from similar circumstances have achieved. With the input data (40+, masters) the range of possibilities is quite large.
"Faking it till you make it" is perhaps not an accurate description. It presumes you need to prove something to someone. A person just needs to find the thing they like doing, and then thrive in doing that. Once you thrive people will notice anyway. There is nothing wrong in starting humbly, and then moving upwards once skill and confidence builds up.
The post I was replying to said "look at all these people who did stuff in their 40s". I was simply pointing out that this is NOT who OP is, based on his post. And he should not be thinking that, unless he wants to fake it till he makes it.
Accepting the reality, that he's done nothing for the last 10 years, SHOULD get him to pick something, anything, that he would be proud to build up over the next 10 years.
Pretending he is similar to Steve Carell does him a disservice.
