Bare in mind, not all gyms will compete L4 but in the USAIGC they actually can compete a L3 they have made for that system. Some gyms do mock meets for L4 but they are officially on team while some are not.
A couple of our current L4 have been in gym for 6-9months. It's been and good and bad. I had one L4 last year barely in gym and he only got onto team for about 6 months before season and was practicing only 1-2d at 1.5-2h and he managed to get 8's mostly and a few 9's ( except on PH which he didn't compete till the end of the season ).
You should also talk to his coach and maybe some other boy's parents.
In my skill system, most L4 skills are required to be finished in L3 and say for L5 skills in L4, etc. Not all, but many. Many gyms will have their own skill systems in place that may not be in line with the USAG system.