Agility is about body control and coordination. If you get an agility ladder (there's a skilz brand one for $25 on amazon), you can make it challenging in terms of fitness and coordination.
Another good drill is a adjusting step drill in a figure 8 pattern (make figure 8s around 2 obstacles - I use comes, but have seen water bottle and ball cans used as well). Start with an easy work to rest ratio, then make it more difficult as his fitness improves (10 secs work, 20 rest...20 work, 20 rest...you get the idea).
Prince Rebel 95
PTR Certified Pro / USRSA Certified MRT