I am late 20s and feel like I have never been confident in both career/work and making life plans.. like I have been coasting through unsure what I want to do, what I can do etc.
This is okay. No man is born wise. No man is born to a mission. No man is born knowing all the answers. No man is born with a plan. No man is born with a philosophy. This is okay.
Reaching a particular age and not having accomplished the same things or some thing of equal perceived awesomeness as some other person your age or a similar age does not make you a failure. Yes, everything in your life is your fault but this is also what makes us free. I'm sure you've heard the cliche (you have to know your cliches, they're your friends) "Freedom isn't free." When we own the things that are on ourselves we're paying the price of our freedom.
I sound very flippant here but that is not my intention. I was a mess at 28. I'm still a mess at 50. I'm just a different kind of mess. The difference is I now much better understand which parts of the mess are on me and which aren't and what I am and am not willing to do to reconcile them. I better understand what I am and what I am not willing to live with.
The other thing that is different about 50 than 28 is that I know how important it is to ask the right questions. There are always answers. You've gotten an entire thread of answers. But have you gotten the questions you need to ask?
You can't picture yourself as successful. Do you know what you would consider successful? Do you understand the price to attain that definition of successful? Are you willing to do that? Are you willing to change your definition if you're not willing to do what the first definition requires? Why do you consider yourself not successful? Why do you consider yourself not happy? Why do you need a "life plan?"
Even those might not even be the right questions.