Is it permissible for a person to sit with a girl he is engaged to, and the engagement has been announced and the ring exchanged, but the marriage contract has not been concluded due to her young age?

The fiancée, before the marriage contract, is a stranger to the suitor. Therefore, he is not permitted to be in seclusion with her or sit with her unless a mahram (definition) is present. She must also be modestly dressed, for the Prophet, peace and blessings be upon him, said: "No man is to be in seclusion with a woman unless a mahram is with her." Furthermore, exchanging rings before the contract is a forbidden custom due to imitation of the disbelievers and touching what is not permissible. A Muslim must adhere to the etiquette of Islam and establish his home upon piety.