Actually your weight should be proportional to your height. The woman on the right is probably taller.
If there is so much pressure on society to be thin, why are we all getting so obese?
Your weight is important especially as you go into your late teens.
Being overweight can literally ruin your health as you get older with an increased risk of about every health problem imaginable (cancer, heart disease, joint problems etc)
Our bodies have not evolved to deal with an excess amount of weight. Once you become overweight the first time it becomes a lot more difficult to keep a normal weight for the rest of your life.
Obesity is the biggest problem facing national health today and we spend billions of pounds dealing with the effects.
EDIT: Can I also point out the woman on the right looks like she lifts weights (notice the abdomen). Personally I would rather be with somebody who actually cares about their health than a woman who would rather spend a few hours watching TV on Friday nights.