A 24' extension with a 180 degree turn would give that turned end a lot of leverage against the person holding the pressure end.
I sure hope the gutters are still attached to the roof/soffit really well, could have the gutters falling down towards you pretty quickly, especially if they are already full of years of built up, well set, stuff and you add another 1600 psi of force against the nails that hold the gutters in place.

Have you given any thought about where all the stuff that was in the gutter is going to go after it leaves the gutter?

Holding onto the 1600 psi wand with a 24' extension, blowing water against a floppy loose gutter while dodging the flying gutter debris, could also become a big game of dodge the falling gutter and its leaf content. Be sure to catch the event on video, it could be worth some money, or at least a good laugh after you recover from treatment. We wouldn't laugh at such a video if it became available... we promise..... Gene