If there was another 5 years on each of them, nobody would think twice about it, even if the genders were reversed.
If the 24 year old female was in a supervisory situation over the 16 year old male - even if they were working in a fast food joint - there could be repercussions. If there was a mentorship or leadership role on the part of the female in activities where the teen male was a participant or learner, it could be viewed as sexual abuse. It all depends on whether there is a perceived power differential between them.
Whether or not she keeps the baby and expects him to pay his $hare (hard to to when you're 16 with few marketable skills) of the child care expenses, is between the two of them, and depends on the amount of emotional and financial support they hope to get from their respective families. They could always put the baby up for adoption too.