Opinionated yes, regardless of them being immature or not. But i think being opinionated is quite common trait for all T types, however i think Ti types more often have rationale to back up these opinions, while NTJs rely more on intuition and rather unconscious Fi to form opinions, which means that there isnt so strong rationale to back up the opinions, but is more based on feels and intuitions about observable Te/Se facts. I have seen it quite a lot that INTJs come up with rationalizations to back up their opinions, but the rationalization is usually just some rationalization made up later to justify the actions taken based by opinions(which sometimes are rather funny, because they dont make logical sense, as its often trying to put logic to something that inherently is not logical), rather than the actual rationale that was used to form the conclusion. However i suspect that sometimes making up this sort of rationalizations later is just trying to mask the irrationality in the INTJ that s/he doesent want to show to others(sometimes its a mask for self, not just to others, but in this case the INTJ actually believes the rationale), as it would make him look weak to others or as a self-defence mechanism of the ego to not to look weak to self. NTPs do often have more opinions about things, but its because of Ti forming these opinions and they are more often based on thinking, but ofc there is an element of assumption from Ne, interpersonal value aspect of Fe and subjective factor of sensing that might take this Ti analysis the wrong way. But this also makes it that if Ti is proven wrong, the opinion is changed more easily since the aspect of T rationale is stronger and "deeper". While NTJs dont change their opinion that easily based on reason, but it needs more of their subjective N and F to change to change their opinion. Sometimes it might change easily regardless of external things or rational analysis, but for someone else to change this, it requires more rationale from external world(as more reasons or excuses are formed from NiFi to try to take down this rationale from others), because the opinions are more deep rooted in Ni and often rather unconscious Fi than Te.
INTJs can get loud if they are in the heat of an argument and in safe environment, or if someone else in the similar situation is talking and they want to talk too, they can talk over and louder than the other person. But being loud in general is something INTJs are not.