“Up to the age of “ and “below the age of” have the same meaning. The most natural opposite would be “over the age of” but you could also say “down to the age of” in certain circumstances. Normally the training center serves elite-track gymnasts over the age of 10. But the directors can make exceptions and have taken athletes (down to the age of 8, as young as 8)

Thank you

Solo se puede decir “below the age of” o “under the age of”