In a story written in past tense, is using present tense grammatically correct in the narration?

For example, just something quickly made up:

Sam started to run from the house to the nearby forest. The freezing weather caused him to shiver, but the warmth from running very rapidly heated up him. Sam, son of a lumberjack, is/was 16-years-old this year.

Given a context like that or similar to that, for the bolded text, which is one is correct? On one hand, "was" seems to be the correct one as the narration is in past tense, so for consistency, everything should be in past. But on the other hand, "is" also seems to be correct because he isn't "was 16-year-old", he is 16-years-old.

Thanks in advance for any answers, and if possible, please point to a resource I can study.

Solution 1:

In my experience, in fictional narration of the past, using a past tense is generally the norm for narration of events or for indirect (reported) discourse. Direct speech, however, should take the tense that the speaker (or thinker) is actually using.

Contrast the following:

Indirect: Later that night, Sam thought about the fact that he was now sixteen years old.

Direct: Later that night, Sam thought to himself, "I am now sixteen years old."

There may be exceptions, but I can't think of any at the moment.

Note that in certain types of non-fiction, the rules may be somewhat different. For example, scholars in philosophy will say things such as: "In the Metaphysics, Aristotle again writes about matter and form." One reason the present is common in philosophy scholarship may be that the focus is on perennial ideas rather than on the fact that the actual expression of those ideas took place in the past.