If you line up all the eggs from each hen, from the first one laid on to the latest one, you will notice each subsequent egg is just a tad larger than the one before it.
I noticed that this year, my pullets' eggs have all been larger from the first, and they've gotten to be full size quicker than previous batches of new layers. The difference this time is I refrained from supplementing their light exposure until they were almost seven months old. This gave them more time to add to their size before using their energy reserves on egg production.
In comparison, the three little pullets I raised six weeks behind these began to lay within days of this first batch of pullets, and their eggs were all quite small. I can only conclude that the younger the pullet is when they begin laying, the smaller the first eggs will be.
Any others notice this correlation between age and egg size?