What Does "4 Months" Actually Mean?

mrsj0423

Okay, I apologize in advance if this an idiotic question, but when people say "...you can start solids at 4 months..." or "blah blah blah at 5 months...", do they mean at the start of said month or once LO has completed that month?  Like right now DD is 3 months.  But really she has completed 3 months and is beginning her 4th month of life.  They say that stage 1 solids can be introduced as early as 4 months if baby shows signs of readiness.  Does this mean now, or once the 4th month is complete?   I guess there are some instances where it would be more helpful to break things down into weeks, this being one of them.