I think it is a bit extreme to have that many kids and to keep having them at their age, but at the same time I am fine with it b/c I do believe it is completely their choice and admire their faith. Actually I'm kind of jealous b/c we have similar thoughts about childbearing and we will never probably have as big of a family as we wanted.
DH and I do not plan on ever preventing, but we obviously aren't popping out kids every year. We were planning to do NFP eventually between kids if we ever wanted a bigger age gap, but since we have MFI I don't think we will ever have to worry about wanting a bigger age gap....we never prevented at all after our son and he will be older than we ever imagined before he gets to be a big brother. We always wanted 5-6 kids, but at this point we will take as many as we can get and see them as a huge blessing. I'm 26, so we have a ways to go until menopause. I doubt I will even end up with as many kids as we wanted so I'm not to worried about being the next Duggars