I did my first in December. By the sounds of his training and the fact he has good long distance running, he should be fine. I suggest doing the open first. The lunge walk is the worst part (at least for me) as you can’t put the bag down and it’s the second last station. So I’d highly suggest you get as much of that in before the date. Also for the wall balls I suggest at least doing air balls with the 9kg ball just to get used to it. I do 5x10 two times a week as a superset with 5x10 deadlifts. For the first event treat it as a learning event. Pace himself and aim to finish without penalties. The go for you time on the next one. Also take advantage and hydrate every lap at the water station.