Final answer:
The words 'old master,' along with the context of performing errands and having limited leisure time, provide evidence that the author was enslaved.
Step-by-step explanation:
The words from the excerpt that provide evidence that the author was enslaved include "old master" and phrases that depict the author's lack of agency and subjection to the control of others, as seen in duties like "run of errands" and descriptions of his life at the plantation. The term "old master" directly indicates a slave-owner relationship, which is an explicit reference to being enslaved. The context of having limited "leisure time" only due to being too young to work in the fields also suggests the forced labor conditions of slavery.