The assumption that you are making here is that with the same motion of a punch, that you are applying $\text{100 N}$ of force to both a wall and to the air. However, you should think about the most fundamental equation of Newton's laws, namely,
$F=ma$
The most important part of this in relation to what you are talking about is that the force applied, $F$, is proportional to the acceleration, $a$. When you hit the wall, your hand goes from full speed to a complete stop rather quickly. This is a fast deceleration, or a high value of $a$, so the value of the force is high.
However, when you punch through the air, the air molecules hardly slow down your hand at all. This means that your deceleration is low, or a low value of $a$, meaning that the force, $F$ is also low.
In the absence of a wall to stop your fist, what is really stopping your punch is your own body, not the air, as your arm socket will have to pull back on your arm to keep your fist from flying away. This also will slow down your arm more slowly than a wall however, since the tendons and ligaments in your arm tend to stretch, reducing the deceleration compared to the wall, and thus the force.
So, what I'm trying to say here, is that yes, the forces are always equal and opposite which is in line with Newton's laws. However, your assumption that force from hitting a wall with a punch is the same as a force from swinging your fist through the air is incorrect.
I hope this clears things up for you.