Mid Single Wards already exist! I know this for fact because I am a member of one of them. I know that there are only 9 or 10 of them in the church, but California and Arizona both have at least one and Utah has three of them that I am aware of. The age span is 31-45 and I think that is the perfect span. Once you turn 46 you are out of the ward but at that point you are welcome to be a "frequent visitor". And YES, IMHO, there should be an age limit!!!