age gap between #1 and #2, 16 mos. unplanned, great nursing preg, fantastic tandeming, i nursed them together all the time.
age gap between #2 and #3, 31 mos. planned, we wanted to wait until #2 was 2 in case any weaning occured. we jumped started by 2 mos since i knew alot of mama's IRL that had trouble conceiving when they planned. i got preg right away. nursed both during the entire preg even when nauseated and vomiting (water is hard for me to drink in the A.M. when preg, and that really effected supply). tandemed all 3. worked out pretty well.
age gap between #3 and #4, 19 mos. unplanned. #3 was nursing almost exclusively (not too interested in solids), and still nursing the first 2. i was a little worried because i wanted #3 to get all the benefits her brothers had/have. after 1st tri, it was bothersome to nurse the older ones, but not the youngest. all 3 nursed thru the entire preg. the age gap between youngest and oldest is 6 1/4 yrs, but all are still nursing today.
in my case, planned spacing or unplanned hasn't prematurely ended any of my children's nursing. in might have prolonged it, i don't know. for me, the younger the nursling the easier it was to nurse through a pregnancy. i did nightwean my first 2 during preg with #3, just before i found out about CLW on MDC. i hadn't factored in nightnursing when planning #3. i guess before i heard of CLW, i just figured my nurslings would nurse as long as they needed to without really thinking of how i encourage or discourage it, just following instincts. ironically #3 self nightweaned just before #4 was born. she was younger than her brothers when i started weaning them at night.
my favorite age gap is the 16 mos. i don't believe that's there really is an "ideal" spacing especially since every family has entirely different circumstances. i'm facing 40 this summer and will probably be nursing well into my late 40's if judging the last by the first. but, i do love tandeming and am so greatful it has worked out well for me. not sure if i'm a true CLW'r, but i've got happy, healthy, breastfeeding children