I was actually pushing it this summer with trying to reach a point where I'd call myself overtrained. 7 days per week, multiple sessions each day. There was when I literally trained TBT 5-6 times per week, and yet: no sign of overtraining.
I sometimes feel shit (like an hour ago) but that's more due to the heat what we have right now. When indoors, everything ok, only in the 35+celsius heat in a concrete yard without shade. Well, that's another thingy.
As long as nutrition and rest is adequate, your body is capable of more than you could imagine.
Take Synergy or Paragon for example. They use awesome amount of volume-intensity, and even frequency. They have lot of responsibilities outside the gym, a stressful life. Yet, they maintain what they're doing, and they all have strategies to ease off the pressure a bit when they feel a bit over the edge.
Through their example one can easily see that it's all about mindset.
PS: Synergy and Paragon: sorry for mentioning your names, but whenever it comes to "overtraining", I always get you two in mind in the first place. Again, sorry.