Final answer:
Without a reference to Aven's grandmother in the provided text, it is impossible to determine her age. The excerpt mentions a character named Lassiter, who is thirty-eight, but that does not help us infer the age of Aven's grandmother.
Step-by-step explanation:
The question pertains to a character named Aven's grandmother, who lived in a trailer in Kansas. Yet, based on the reference provided, there is no direct information given about Aven's grandmother's age. The excerpt speaks about a character named Lassiter, who relates his experiences over the past eighteen years and reflects on his age. Lassiter mentions being only twenty when he started on the trail, and thus, if this is the character in question, he would be thirty-eight years old at the time of the statement. However, without specific reference to Aven or her grandmother in the provided text, the main answer cannot be deduced directly from it. Therefore, to accurately describe the character's age, more context or information from the text would be required.