Loca looks a LOT like my Little Cat, who looked about 6 months old when we got her but was apparently 2 years (the vets can tell by the teeth.) She had just had a litter when we got her from the TAS. She was only 4.5 lbs when we got her, but quickly started eating and chunked up (now a healthy but small 5.4lbs) - you'd never know by looking at her though that she was older than 6 months, and she's still pretty playful. It could be that Loca is just discovering the joys of food (like Little did) and is eating too much?
My first thought was that your kitty might also have worms, but I guess you'll find out soon.
I know what you mean about it being a little appalling - our first vet for our fat tabby told us that Turdlet might have a leaky eye due to chlamydia! He was 3 months old!! (Apparently it's not an STD in cats though?)
4 years later and he still has a leaky eye....
Good luck, and let us know what the conclusion is!