Disregarding age differences, especially in the context of friendship (often used as a modifier for 忘年交 wàng​nián​jiāo or 忘年之交 wàng​nián​zhī​jiāo)

Connects a describing word or phrase to the noun it describes, similar to 的 de but used in formal or literary writing.

good; fine; nice; satisfactory; (of people) close or on intimate terms