Re: wasn't Jane Ireland too young?
I can't tell from your post whether you have read the Macy article refered to in my post of anno 2000?
It's too long ago now for me to remember the details but I can say that Mr. Macy's genealogical credentials are prestigious [please Google on Harry Macy, Jr] and that no additions or corrections to the article have since appeared in the quarterly New York Genealogical & Biographical Society Record.
Possibly Macy directly addresses your concerns in that article. His statements and proposals will have been fully documented to the highest modern genealogical standards. But, this does not mean that his work should go unexamined.
So, I don't mean to sound dismissive of your query. Indeed, it is a good question and needs to be addressed.
I have not read the Best-to-Ward discussion, nor the Thomas Ireland will you provide a link to (unless it appears in Macy's article, but is since forgotten by yours truly), but have to wonder if the decision that Ireland's 1668 will "showed Jane (his second daughter) was not yet 18," is a simple misinterpretation of the wording and/or terminology in that ancient document.