Translate su amigo de muchos anos in English?

The most accurate translation of "su amigo de muchos años" depends on the context and the level of formality you want to convey. Here are some options:

Formal:

* Your long-time friend

* Your friend of many years

* Your longtime acquaintance

Informal:

* Your old friend

* Your buddy of many years

* Your long-time pal

More specific:

* Your childhood friend (if the friendship started in childhood)

* Your college friend (if the friendship started in college)

* Your friend from high school (if the friendship started in high school)

The best translation will depend on the specific situation and the level of formality you wish to use.