To tell someone your age in Italian, "I am seven years old," you'd first conjugate the verb 'avere', say the number, and then end with 'anno/i'. "Io ho sette anni."
Another example: "She is 12." = "Lei ha dodici anni."
Soltanto means 'only'. Appena means 'just''.
As far as I understand, appena would be used more in the meaning when someone has 'just turned' seventeen. Someone please correct me if I am wrong.
I am quite sure you are right. In French, the idea of "hardly, barely, just (now)" is translated by the adverbial phrase " à peine" = apena (Italian). HTH♡
Re: placement of only in translation for which i was marked wrong. Yes, the meanings ate a bit different but saying " she only is seventeen" should not be wrong