How is the name Jesus in the bible if J is only 500 years old'?

The New Testament or Christian Greek Scriptures were written in Greek and Aramaic languages.

"Jesus" is an English version of "Ye·shu′a" of The Bible.

Since the English language has evolved greatly over time, with major shifts in creating a written language over the centuries, we transitioned from Old English to Middle English (think King James) to Modern English.

So, there really is not any concern over the English use of the name Jesus and the use of the letter J.