In order to talk about age, we need to use the counter 歳. Please note that 歳 is only used for talking about the age of living things like animals and humans. You would not, for example, say: あの車は何歳ですか？.
As with the previous counter words you have learned, 歳 has several irregularities in how it is read in combination with certain numbers, as shown in the table below.
|one year old||一歳issai|
|two years old||二歳nisai|
|three years old||三歳sansai|
|four years old||四歳yonsai|
|five years old||五歳gosai|
|six years old||六歳rokusai|
|seven years old||七歳nanasai|
|eight years old||八歳hassai|
|nine years old||九歳kyuusai|
|ten years old||十歳jussai|
|eleven years old||十 一歳juu issai|
|twenty years old||二十歳hatachi|
|thirty years old||三十歳sanjussai|
As you can see, twenty years old is an exception, and after that counting tens continues as expected.
Below are several example sentences relating to age.