Nikki is right (again) responsibilities are about alot of things, not only ur mental, physical, or finanical. Though ur might want a baby, but do think about it though, ur aunt's baby is her baby, u only baby sit him, it's not urs, so it's 100 times less stressful!
I am not saying u shouldnt have the baby, but at least really think with ur brain before making a decision in which u might regret. Becoz thinking with ur biological clock is not wise.