I wonder if our paths crossed on MN Red? 
DH was 34, 36 and 44 when ours were born, I was 28, 30 and 38. Our youngest is now 12, the eldest is 22, so DH and I will be similar in ages to you and your DH when the youngest is in his early to mid twenties. I left MN because I felt it was becoming increasingly vicious (or perhaps I was just outgrowing it) and because I felt I’d been through the child rearing years - it was quite odd being on there with young mums who were the same ages as my elder 2 (and younger in some cases). I suppose I’m caught between MN and GN but feel there’s more to learn from posters on GN who have been through the stages I’m now going through.