It's totally normal.

So, Dr. AJ Drenth in his book charted the function development timeline (theoretically) of the types.
The tertiary function develops around the age range of 20's & 30's. Within that range, individuals differ dramatically according to life needs. It takes longer to develop these lower functions.

So for INFJs, Ti is the function that's really stretching it's wings and growing in the 20's & 30's.

Ti is serious in nature, often presents as cynical & doubting, and it contributes to aloofness, solipsism, and second guessing.

While all of that sounds a bit negative, the truth is Ti is an absolutely vital tool that we need to counter our other functions. It has a very beneficial side, and the sooner it develops fully, the better.

So the best way past this stage is through it! Don't deny the growth progression by trying to be like what Fe tells you you should be like. Embrace it and you'll feel better about it and that will help you feel a little more relaxed around others.
This is you, growing.

Also, keep in mind the friends you spend time with. If someone in particular causes you to clam up more than others do, there's probably a very good reason. Sadly, it may be better for you to discontinue that association if it isn't good for you.

 

I am more serious around others than I used to be but I find it only really becomes a noticeable problem around people I'm not comfortable with. Then that serious aloofness is almost like my armour against them. I just go into defence mode without even meaning to and I can't turn it off despite being internally horrified at how cold and quiet I'm being.

It happens when I feel like the people I'm with wouldn't like/appreciate/understand my normal self, or when I feel like they're not showing me their real selves. Both situations are a form of distrust on my end. Me not trusting them to like me, or me not trusting them because they're being deceptive (even though this aloofness of mine is equally deceptive).

It's also really hard seeing people interact more comfortably with others in front of you. I found that made it so much worse. Here I was, being aloof because I was scared those people wouldn't like the real me and then they'd act aloof toward me and warm toward everyone else. It was probably a response to my own behaviour toward them but it just made me feel like I was right about them not liking me! And then I'd double down on the aloofness.

I have no solution for it. You can try to establish (or in your case reestablish) intimacy and comfort slowly or you can stop being around people who provoke that response from you, as Rebecca said. I've chosen to stop being around them. Because I'm only like this around certain people, I do think it can be a sign of a deeper incompatibility.

 

I know that I can be quite aloof. I can also be timid so this may be interpreted as detachment by someone who doesn't know me that well. Not all of the time but I have gone through phases. Usually, when dealing with stress for long periods of time. I become more internal, keep to myself, and start to distance myself from people.

There are multiple sides to my personality. When I don't feel like I can be completely show parts of myself around a person, I may be aloof and detached. It is not really conscious, it may be somewhat of a defense mechanism. Also, around people who I don't know as well. It may be an aspect of yourself but it doesn't necessarily define you. It can be very difficult when you cannot always predict how you are going to say something. Sometimes when people misinterpret my inflection, I get mortified.

 

There may be nothing wrong but I do find it odd you are like that with friends
Are they close friends or something else

I think all that has happened is you have been spending a lot of time in specific subjects and the subject of other people/social activity has been kind of put away in the freezer. I would say that is normal.
This is how I was when transitioning into a new work environment, more open than I was previously used to. It took time for me to adjust my physical body... to get into a new habit of being.

 

when did you notice the shift towards aloofness? did it accompany a happy or disturbing or monumental event in your life? are you currently craving time alone?

 

Why are you afraid of saying something hurtful? Do you have a history of doing so? Do you have the desire to?

Consider telling your friends your concerns and how it's affecting your behavior. They may not understand but they should be understanding. If you want more than superficial conversation, try bringing up topics that interest you and you suspect might interest them. Withdrawing is only likely to make the problem worse.

 

Yep, when I was younger (11-13) I said things that to me weren't hurtful, but others got offended from them. Basically back then I was a different person. I think now I am a lot more aware of others' feeling (seem to have developed Fe).

when did you notice the shift towards aloofness? did it accompany a happy or disturbing or monumental event in your life? are you currently craving time alone?

It was a progressive event. I'd say that at somewhere in the past I got a series of unhealthy things that happened to me in a short period of time. That's when it started developing.

I think I am afraid of saying something rude to something, so I keep things superficial. What fascinates me how easy some people get behind the fence of that superficiality, while to me it appears as a thick wall, near impossible to break..

 

On the "lie down with dogs, get up with fleas" principle, I become aloof when people disappoint or disgust me.

If that's a bad thing, then I'm content to be bad.

 

Aloof was the first word I leaned that applied to me. I looked it up in the dictionary after the teacher used it in class. I always wondered why I was different to other people.

I was now officially “Aloof” It was quite thrilling to think that people looked at me and thought “wow! he is so Aloof” I was now in the minds of other people and not alone any more. I kept saying it over and over. “aloof, aloof, aloof, aloof”

I love that word