Since there is no SCYSA U12 league, there is very likely no reason why CUFC95 could not play U13 Classic and Snadlapper U12. However the point most teams/clubs make in playing up to U13 is competition but also 11v11. U12 Sandlapper is 8v8. Roster are limited to 18 for 11v11 and 14 for 8v8. if CUFC has 14 or less players they can do both.
As far as within SCYSA I believe ( not sure) that you can only play one age level in a season. It was my understanding that you nmust compete in the state championship of the age level of the state champioship season. Thus a U14 playing up in U15 in the fall must participate in the u15 state championship.