I [am] three years of age
This breaks apart as follows:
- 我 (wǒ) = me
- 三 (sān) = three
- 岁 = years of age
- 了: I understand 了 here is the change-of-state 了: prior to turning 3, I was not 3, so that state has changed.
I have two points of confusion regarding when it's correct to say 我三岁了:
- Two years old: 我三岁了 is incorrect because... (why?). It seems correct to say e.g. 明年我三岁了. It seems theoretically possible that 我三岁了 could refer to a future change of state (although surely none would use it because it's misleading).
- Three years old: 我三岁了 is correct: I turned 3 (change of state). [more about this in point 2.]
Four years old: 我三岁了 is grammatically incorrect: my best guess as to why is because while I turned 3 (change of state), I subsequently also turned 4 (unchange of state). With this reasoning, 我去年三岁了 is self-contradictory (maybe?). And Baidu indicates it's correct to say
Last year, I was three years of age
without the change-of-state 了.
When I'm three years of age, for that full year, I'm not sure if it's okay say 我三岁了. For example, I wonder if it's okay to say
I [am] three years of age, tomorrow I [become] four years of age
The change of state happened a long time ago, so I'm unsure if it still counts as a change of state (but maybe a change of state has no expiry).
Question: During which time in a person's life is it correct for them to say 我三岁了 (I am 3 years old)?