RE: When should I start going to the GYM ?
weight IMO means nothing
so say 3 months time you are 75kg
scenario 1 - you have eaten in a calorie surplus and gained weight but have not been physically active - you are not at a more acceptable weight according to 'medical guidlines'
scenario 2 - you have eaten in a surplus but have gone to the gym and built some lean body mass, not all lean but mainly and some body fat. you are now more active, have more strength and are more effecient as using calories and not storing them
IMO its a no brainer
one - eat healthy and try not to add much weight and dont train, ensuring all macro and micronutrients are catered for
two - eat more, eat generally clean (as above), gain weight but actually go to the gym, lift 'heavy weights' with a structured plan and gain quality weight
the bastard child of both is IMO not the place to be (no new muscl, more weight)