There has been quite a few discussions of heart rate on this forum. From what I have gained discussing this with various doctors (off their shift and informally, though), there is a HUGE variation between individuals as far as max heart rate goes. I am the same age as you (27) and the max I have held for a minute is more around 220, way beyond the predicted 193. This used to scare me (I'd stop counting my pulsations in aerobics classes and lie about my heart rate when the instructor would ask!) but I have learned that it's just me and that I should live with that. On the other hand, it would be ridiculous for me to train at 145, I don't even feel anything at that point.

If variation on the higher side is normal, I do not see why variation on the lower side wouldn't be, and I'd be cautious with trying to voluntarily push things further than your max. Maybe you just have a stronger, bigger volume heart. However, taking the heart rate monitor on a favorite hill and climbing it energetically will certainly be an interesting test. Just make sure you go with someone and don't push to the point of passing out. Feeling a taste of blood in your mouth/having to vomit is an indicator that you should stop.

So "listen to your heart" and ask a sports medicine professional if you have a chance.