I've had a discussion with the parent of a very small guy who is a terrific athlete (not baseball), about this matter. Around here a couple of parents have sent their kids to private school to repeat 8th grade. That allows them to gain a year of physical or other maturity, and delays the start of the 4 year clock of eligibility in our state. Once you've started 9th grade, your eligibility is running out in four years even if you aren't playing the sport. The only way to get an extra year is to do a PG post-graduate year at a prep school.