What does the number of leaves mean????

Ok so here is my question i have a few plants and they are about 2 1/2 weeks old and starting to look pretty good for a first grow, they are agetting sets of leaves with 3 leaves my main question is what is the difference between 3 leaves and 5 leaves or is this an age thing where as they get older they start making more leaves and so forth? i am a total newbie, so i am really sorry if this is a dumb question i just thought i would ask in hopes someone could give me a more educational thought to it.
Thanks to all of you who are of assistance and who try to help so many of us newbie people. with out you we would be lost.

any body have any clues please any help would be great.

its just how they grow. 3,5,7,9.............

oh cool thanks. that makes me feel better than i am not grownig mutants.

No prob. glad to help.