Final answer:
Cicero wrote 'De Inventione' around 81 BCE when he was about 25 years old. This early rhetorical work contributed to Cicero's reputation as a master of Latin prose and had a significant influence on literature and philosophy.
Step-by-step explanation:
The influential Roman philosopher, orator, and statesman Marcus Tullius Cicero (106-43 BCE) wrote De Inventione when he was quite young, around the age of 25 years old. This means he would have composed this work around 81 BCE. De Inventione is a treatise on rhetorical theory and was written during Cicero's early years before he moved on to the more mature and philosophical works he is known for, which greatly shaped Latin prose and the Roman style of rhetoric. Not only has Cicero's extensive body of work—surpassing any other Latin author in terms of volume and diversity—had a lasting impact, but his philosophical works have underpinned moral philosophy through to the Middle Ages, and his rhetoric influenced European political leaders and the founders of the United States.