Hi. I'm an "ISTP" and I related to this quite strongly. This is a mini rant about myself because I'm feeling particularly opinionated today. I pooped this out in just a few minutes and it mostly applies to me but hopefully you can relate to it a bit, so here goes.
Same thing here. I was INTJ on the nose 3 years ago, now ISTP applies to me way more and I'm almost 26.
Turns out I was just insecure, overthinking, over analyzing, had a huge ego (because I knew I was smarter than most everyone and identified way to strongly with that knowledge. I mean, I had fucking proof didn't I? SAT Scores, not learning anything in school at all because I already knew all that stupid shit, etc) and constantly "Ti/Ni looping". I was figuring myself out. The whole thing has honestly given me the opinion that MBTI is bullshit (and psychologists will agree) and basically your "personally type" will often just reflect how at ease you are with yourself and secure with yourself you are, among other things. Especially with those crappy multiple choice tests. This is why it changes with age, etc. So here I am now a "Sensor" and really it was just all the over analyzing, searching for information and learning consistently brought me to a final conclusion that I eventually was forced to accept and internalize; that it's all pointless. There is no need to read between the lines when everything right in front of you is good enough. Other people are stupid and you give them too much credit, they're not all thinking as multi-variably as you think they are. Just be confident in yourself. There is no need to figure out who you are, and don't try to "be" anything. Just be. Trust you're incredible mind to take care of things, it'll intuitively learn as you go and adjust naturally.
If you're getting INTJ and ISTP you're likely smart and logically minded, so just go out and tackle life. You'll be amazing how things work out for you when you keep your eye on the ball and just believe you already have the tools to do what needs to be done. Slowly but surely develop discipline and confidence. Nothing needs to be learned, you already know how. You'll become more social, people will like you, you'll have more important shit to worry about as life goes on, and suddenly you won't be INTJing your way through life because you have more important shit to worry about than some obscure worthless piece of nonsense knowledge that doesn't fucking matter. Or even if it does matter, you will be happier than studying Physics 12 hours a day by yourself in your room with your only hobby being League of Legends. Many people will think you're not as "smart" but really it's because you already went through that over analyzing dick measuring contest. You realized it was fucking stupid and there was no point, it doesn't matter how "smart" most people think you are, thats your ego dying for acknowledgement from those around you. Stop personally identifying with it. If you're actually intelligent it will shine through without you needing to pump it up. Ask yourself, if you're so "smart" then why are all the "dumb" people out there taking over the world and excelling in business, personal endeavors, relationships and any other goals they may have? Because they're smart enough to do what works, and what doesn't work is learning a bunch of pointless information construction an outer fake shell of knowledge to impress people with. The real leaders in this world are not as shallow as they appear. Getting things done in the real world is what "works". Many people have a weird sense of confidence naturally because they were just stupid enough to act cool from an early age, but if your a smarty pants you likely had to find it and WORK for it. You're advantage is now you're smart AND confident. You'll go much farther than all the dump people that just happen to fit in all their lives. Your ceiling is much higher. You'll have learned how to act just dumb enough to fit in, all while your mind churns away in the background figuring out what needs to be done. What actually matters. And it sure as shit isn't this MBTI garbage.
Goodluck.