B fund is defined contribution. It doesn't care how old the recipient is so an older newhire is not cheaper. Based on insurance costs and sick use an older newhire is probably more expensive.

Hire a 21 yr old, or other young guy, over a 25, 30, or 35 yr old who probably has more experience and maturity? Probably not. But there are always exceptions, especially for young, focused, driven, and talented candidates with impressive resumes for their age.

Good luck to all.