Geckos, like people, all vary.
120lbs on one 5'6 girl might seem ideal, and 120lbs on another 5'6 girl would look horribly thin. I weigh 180, at 5'4. My doctor told me to never drop below 160. My littlest sister is taller than me at 5'7, and weighs 130ish. She needs to loose around 10lbs, too.
I had full grown adults around 50g, others around 110g. The only way to judge if they're fat is to see a photo.