great experience!

Modern american english would use eldest instead of firsdborn, which is relevant to serious Christians from the Old Testament references, as the son of this person, and his son and so on, with the eldest being stress as the first born or a woman or man.

It is old school and modern cultures have wiped out the relevance of being the firstborn because of the introduction of mass education in schools instead of learning just from one's elders only as many of us did in previous civilizations and births.

If however you use firstborn, it is best to put in a line or two stating from you are culturally endowed with certain ancestral skills as compared to your siblings. Otherwise modern readers may miss that and feel that the term is something antiquated.