The presence of Actin (ACTN) and Peroxisome proliferator-activated receptor (PPAR) gene families is frequently mentioned in literature reports and news articles.

This extends to young athletes as well:

Boys with ACTN3 RR genotype tended to swim faster (25m and 100m) (34) regardless of training status. The R allele was also associated with better 40m sprint performance in adolescent Greek boys (35). Late adolescent girls with the RR genotype performed better on sit up tests than girls with the RX genotype (32). However, the ACTN3 genotype was not associated with several other power or endurance phenotypes in adolescents of either sex (35). Additional correlations between PPARA, PPARD, and PPARGC1A genotypes with standard fitness tests in children were also reported (32,33). Overall, many of these studies associating genetic variation with performance in children have been underpowered and have failed to correct for multiple comparisons, so it is premature to draw firm conclusions. Further, the drive behind the prediction of athletic performance with genetics is primarily aimed at the early identification of individuals who will become exceptional athletes as adults.

That is from Lisa M. Guth and Stephen M. Roth, Full link here