I'm feeling lost

I'm 40 my partner is 31, I'm 6 weeks pregnant, it's his first child and I have 2 from a previous relationship, my girls are 19 and 16 - I'm so scared to be doing this all again, but the stupidest part is I feel too old, I've been focusing so much on TTC that I hadn't thought through actually having another baby, does anyone feel the same or am I just a really bad person?