do the plants typically start smelling before flow...

Yes, some strains can produce quite an aroma, even from a young age and many weeks before flowering commences and while still in vegetative growth. Some will even stink from 2-3 weeks of age onwards and then really stink when in flower, all this is normal and strain dependent. This can be a real problem for growers trying to maintain a discreet garden. Sometimes the only option is to cull the stinky plant to protect the rest of the garden. Strains like "Skunk" have this name for a reason and heavy aroma is often associated with Indica or Indica dominant strains. Hope this helps,.......... Organoman.