Very unlikely that it is the plug.
I know that some people have bikes that will start on the first kick, hot or cold. I have never had one......
The jetting of the carburetor will have a large effect. The engine needs a richer mixture when it is cold so if your engine is normally running a bit on the lean side it would make it harder to start when cold. There is a cold start knob that you pull up that should increase the mixture for cold starting but if that got clogged then it wouldn't do anything, so a really good cleaning of the carburetor might help.
Technique may help a lot. When I start my bike first thing in the morning I have learned that it starts a lot easier if I leave the throttle closed for a few kicks, then just barely crack the throttle and kick until it fires (generally in one or two more kicks). If I hold the throttle open when I first start kicking I will flood it.
Rod
