"Mon monstre a cinq longues jambes."
monstre marin
"monstrueusement haut"
metal legs is translated 'jambes de métal' in French.
deux jambes
I'm not really sure what a "love monster" is... maybe bête d'amour?
Elle a cinq jambes.
Je suis un monstre.
the sock monster would be spelled "le monstre des chaussettes" in French. But it seems a very American thing - maybe French simply never lose their socks?
pigeons ont les jambes
"nous avons mal aux jambes"
His pants fit him like a glove.
There is not a specific length as a person could be "short" and still be considered to have long legs proportionately. (It's hard to explain what constitutes long legs because it's all about the relationship of the legs to the length of the torso.) But, I'd have to say that if your legs are over 8 feet long, it's probably safe to say you have long legs for a 14-year-old.