מִבֶּ֨ן שְׁלֹשִׁ֤ים שָׁנָה֙ וָמַ֔עְלָה וְעַ֖ד בֶּן־חֲמִשִּׁ֣ים שָׁנָ֑ה כָּל־בָּא֙ לַצָּבָ֔א לַעֲשׂ֥וֹת מְלָאכָ֖ה בְּאֹ֥הֶל מוֹעֵֽד׃
от тридцати лет и выше и до пятидесяти лет, все, которые вступают на службу, чтобы делать работу в скинии собрания.
Tosefta Shekalim (Lieberman)
A Levite may only enter the court for service if he has studied for five years, for it is said: "This applies to the Levites: from the age of twenty-five" etc. And further the [Scripture] says: ”From the age of thirty”. If it is said: “From the age of twenty-five” why is it said: ״From thirty years”? If it is said: "From the age of thirty" then why is it said: "From the age of twenty-five"? That means that he studied all the time between the age of twenty-five and thirty, from that point in time and onwards he was allowed to work From here it was said: Whoever does not show success in his instruction within five years, R. Jose says three years, because it is said: "To educate you for three years.