There is no mental development, hardly, visible in his work, only training, undertaken anxiously and prayerfully and with a clearly conceived end.

He designed to write a masterpiece and he would not start till he was ready.

The first twenty years of his life were spent in assiduous reading; for twenty more he was immersed in the dust and toil of political conflict, using his pen and his extraordinary equipment of learning and eloquence to defend the cause of liberty, civil and religious, and to attack its enemies; not till he was past middle age had he reached the leisure and the preparedness necessary to accomplish his self-imposed work.

But all the time, as we know, he had it in his mind.

In _Lycidas_, written in his Cambridge days, he apologizes to his readers for plucking the fruit of his poetry before it is ripe.