Is it true that babies who reach their milestones faster than others are more intelligent? Conversely, babies who are slow in reaching the milestones less intelligent ?

Don't be disheartened, reach milestone early or late never mind - because these are actually more of using the muscle and limbs (I suppose that is what u are referring to). Intelligence has nothing to do w limbs' ability, but active children are able to be smarter(there are many research out there) Milestones seems big issue now. But look at ur LO as a whole. Happy, healthy, active good enough alrdy. Next time can always send them to enrichment classes of all sorts if they like - like music, gym, soccer, ballet etc