Originally Posted by
Iron Maiden
I think what throws a monkey wrench in things is the birth of Franklin and Valeria. Now they both are getting to be as tall as their parents. So Reed and Sue became engaged in Fantastic Four #35, got married annual #3 then Franklin is born in annual #6. Marvel kept him at the age of 4 or 5 for a long time to keep everyone from aging to quickly. Valeria, the one that is now in existence, was born in Fantastic Four #54 volume 3. We won't even get into Sue's miscarriage in Byrne's run and how Valeria Von Doom fits in.
These days it does seem like 15 years has to be the sliding time range but soon it will have to increase. The kids seem to be getting older at a faster rate or maybe Marvel just wants to make that one jump and leave them at their current age, whatever that may be, for now.