When we count the teen numbers we usually accent the first syllable

: THIRteen, FOURteen, FIFteen, SIXteen, and so on.

However, FIFteen can sound similar to “fifty”, so when we say these numbers by themselves we can accent the second syllable instead:
thirTEEN
fourTEEN
fifTEEN.

“I am 30. She is 13.”

For more practice with this concept you can watch my new YouTube video: https://youtu.be/DYdJP3ymZxI