COMMENTARY on 4:6
A. Yusuf Ali:

Translation:
Make trial of orphans until they reach the age 512 of marriage; if then you find sound judgment in them, release their property to them; but consume it not wastefully, nor in haste against their growing up. If the guardian is well-off, Let him claim no remuneration, but if he is poor, let him have for himself what is just and reasonable. When you release their property to them, take witnesses in their presence: But all-sufficient is Allah in taking account. 513
Commentary:

512  The age of marriage is the age when they reach their majority.

513  It is good to take human witnesses when you faithfully discharge your trust; but remember that, however fully you satisfy your fellow-men when you give your account to them, their is a stricter account due from you to Allah. If you are righteous in Allah's eyes, you must follow these stricter standards.