I was 22 when I got pregnant, 23 when I gave birth. Admittedly DH was 27.
He was utterly fantastic and an advocate for me. He definitely did see me poo (very normal and totally fine, make room for the baby to pass through). He was absolutely there for me and on my side. He is a very private man by nature and we never leave toilet doors unlocked etc but it didn't seem to matter. He sat with me repeatedly latching and unlatching DD in front of a full length mirror until we got the hang of it.
Things that helped us be prepared were:
NCT / antenatal classes - knowing about the physiological process of birth and what to expect
Knowing each other really well, including preferences around birth.
Being very clear that I was allowed to change my mind about eg pain relief, breastfeeding. His role was to gently question and help me double check my choices, NOT withhold anything I was asking for with my own full capacity to do so
Planning in advance - if this, then that. Right up to and including maternal or neonatal death. Helped us both feel as in control as possible.
Treating him like a grown up. He packed his own hospital bag. No way was I fannying about putting snacks in for him like I see so many baby magazines recommend.
What happens in the delivery room stays in the delivery room. No mocking the noises I made, no mentioning (even in jest) about "favourite pubs burning down" etc. It was his privilege, not his right, to be there.
Having a back up birth partner for eg if he passed out, got d&v or if he simply wasn't up to the job. Mine would have been my dad and we all discussed this at length.
Talk about the misogyny surrounding women's bodies. I refuse to be disgusted by my own body. (You must refuse to accept his disgust. It's not funny. If he feels that strongly then he has no business having sex or fathering babies.)
All the very best for a boring 7 months ahead OP. A baby! How lovely. 