occurs 95% of the time during the first year or so of puberty in young females, usually around ages 12-15.  This accounts for about 95% of the cases.  The other 5% are women with hormonal imbalances that case their bodies to react like they are back in puberty.  Irregular menstruation often accompanies the puffy nipples, along with mood swings, making them not an attractive option for a monger, IMO.  

 
If you are going to pursue this fetish, then you should be extra careful in getting a reliable proof of age before seeing a girl with this condition or you might find yourself labeled as a pedophile.  If you are successful in finding a woman of legal age with this condition, you may want to check her for weapons when she first arrives at your hotel room.  

There was a poster here who would post pics of puffies.  He went by the name of pornboy or something.