G'day Mark.
The Ace is the perfect first detector (I own a couple of Minelab machines as well, so I don't say that as a Garrett loyalist, but rather, a statement of fact). John from Edmonton posted a how to pinpoint with the Ace about a week back, so look that up for instruction as to how to pinpoint.
Practice with some coins at home. Just put them on the ground so that you can see them, then waive the detector over them and see where they show up on the display. After that, hit the pinpoint button and waive the coil over them and practice your pinpointing technique. Listen to how the audio sounds as you lose the signal. Also get some bits of junk that you recover from your hunts and watch and listen to how they behave on the display (junk bounces around a lot and a good target will give a steady reading or bounce 1 notch (usually). When pinpointing, a good target (and some junk) will give a quick or sudden fade, where as junk items will fade more slowly.
Do your first couple of hunts on a beach or in some bark chipped playgrounds. These spots are easier to recover targets from, so will save some frustration. Just remember, as he will be learning a new skill, he may experience a bit of frustration at first (we all did) but that will pass fairly quickly, and we don't usually post pictures of all the junk that we recover, so when he pulls up junk, that that's just part of the hobby. This annoys some folk, but if your aware of it, then it's not really a problem.
I wish him well and if there is anything that he wants to ask, then just fire away.
All the best.
Mick Evans.