Jeremiah was very young when he was first called by God. I don't think it is certain but some say he was in his early teens between 14-19
Jeremiah preached to the people to repent , or the anger of the lord will fall on them.
Bible says that God gave him his first message in the 13th year of Josiah's reign which was 627 B.C, and preached until the eleventh year of King Zedekiah which was 586 B.C..so it was 41 years
hes 21
Jeremih is 21. I'm not sure when his birthday is but I read that he is 21.