You can use "dalawampu't taong gulang na ako" But to make it formal use "Ako ay dalawampu't taong gulang na"
20 พฤษภาคม 2013
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Dalawampung taong gulang na ako; or Bente anyos na ako. ;)
20 พฤษภาคม 2013
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You can say that in different forms:
1.0) Ako ay dalawampung taong gulang na
2.0) Dalawampung taong gulang na ako.
3.0 BENTE ANYOS na ako (all caps are words borrowed from Spanish which still widely used in the philippines)