Just to add a couple of remarks to Konrad509's answer.
Yes, one of the right answers is: γγγγ―γγ
γγγγ§γγ [watashi ha juu-sai desu.]
In kanji it looks like this: η§γ―εζ³γ§γγ or η§γ―εζγ§γγ
If you wanted to customize your sentence a little bit then I would suggest changing the first person pronoun to something else. Therefore, if you're a girl, you might to use γγγ [atashi] instead of γγγ (η§) [watashi]; if you're a teenage boy who wants to sound cool on the other hand, you might want to use γγ (δΏΊ) [ore].
Also you might want to add γ [yo] at the end of the whole sentence to sound more amiably.
I hope that it clears everything up for you. If you had more questions, you can just write to me personally ;)
Cheers!
In Japanese, "I am 10 years old" is written as γγγγ―γγ
γγγγ§γ in hiragana. This structure features the pronoun for "I", the number for ten, and the phrase for "years old". You can customize the pronoun used depending on your gender or preference.
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