Your story mirror mine quite closely... although my kids are now 26 (girl) 23.5 (boy)and then... yes, a third 18.5 (boy). I was feeling the same incompleteness... everytime I looked in the back seat I just felt like there was one missing. We tried to get pregnant with #3 but it just was not working. And then finally 5 years later... what a joy!
Yes, there is a bit of a gap... and it in some ways is like starting over again... but in many ways it is really wonderful.
#1. You will not be stressed by being torn about who's concert to go to, or which game to attend because of the age spread. (Life has definitely settled down with our last one the only kid at home & still in HS. We have been able to really be involved in his HS activities which is still so very important!)
#2. They can have sibs, yet also have great one on one attention from mom & dad. (Birth order book shows that 5 years gap between kids starts the order over again)
#3. Since your girl is the younger of your older kids... she can be mom's helper, especially if she is nurturing by nature... which you will love so much!!
#4. And from a purely practical point of view... with 5 years difference between your last two, they will not be in college together. I am sure this seems like a long way off but that time will come, believe me, and this fact will be very much appreciated since it is such a relief on the pocketbook!! (We are sending our youngest off to college this next fall just as our middle one is finishing.
#5. We started much later than you... #1 arrived when I was at 34. It has kept us & is keeping us young! Too much fun!
I could go on but will stop now because you get the jist... I give 3 kids and a little breathing room in between them, 5 stars!
Blessings!
PS: I just told my hubby that I could not resist responding to your situation S.... and he said what's wrong with having a third... tell her to have 2 more!