ICS Kindie to Primary

My son was born Oct 2011 so he is not eligible for applying Pre Grade 1 in ICS. May I know if it's better to apply Reception 2 this year or wait until next year to apply PG1 directly as a big boy Are R2 students guaranteed to be promoted to PG1 provided no big troubles found? More chances being accepted in R2 or PG1? Thanks so much for your advice!