Hey, welcome!
Try not to worry about this pregnancy - keep thinking positive! I used to not feel 'pregnant' too for the first few months, right up until I had a bump and could feel it moving. At both my scans I was worried that there would be nothing there, even at my second after I had seen Anna at 12 weeks and kept my regular antinatals so knew she was growing, heartbeat was ok etc... I blamed it on my miscarriage and having seen an empty womb on a scan before, but I think I remember talking to the girls on here about that and discovering it's quite a common fear. It does get better, though!
As for the age gap... My mum had my brother 2 years ago, when I was 17 - and up until then I had been the youngest! She has another the same age as my daughter now and everyone gets along fantastically! I love having a younger baby brother and he obviously adores all of us older kids!

You will be just fine with the pregnancy and delivery - I don't think it will be the same as your last -they say that after so many your body returns to it being like your first or something? And that was certainly true for my mother. Nevertheless, we all do it first once and we all do it fine! I had my first baby 2 months ago and it was a great experience, so you've nothing to worry about!
All the best and good luck with your pregnancy and your upcoming scan

x