How old are fused long bones in men?

Two questions--: If you mean when do they fuse, that is part hormone, part genetic, part nutrition and part life stress--usually 16-19 years old. As you asked it, once fused, you have them the rest of your life...So could be 80-90 years, depending on how old you get!

It depends: The general rule of thumb is that boys stop growing around age 16 (and girls at 14). But, these are just averages and it is not uncommon for boys to continue to grow into college years.