I weigh about 60kg (~130 lbs) and am about 1.75m tall. I've been about this weight since I was 14 or so, with almost no variance. It puts me just on the border between underweight and normal weight based on BMI.
AFAICT, exercise is a fad that wastes an enormous amount of time, and is only worthwhile if you enjoy it. (I'm being a little facetious, but thus far in my life, I see only downside, no upside.)