Learn Russian: Я взял с собой зеркало и увидел, что выгляжу на пять лет старше. - I took a mirror with me and saw that I look five years older.

To express a specific difference in a comparison, Russian uses the preposition на followed by the accusative case for the quantity (here, the numeral пять). This is followed by the thing being counted (лет) and then the comparative adjective or adverb (старше). You can think of it literally as "older by five years."

Why is выгляжу in the present tense when the main verbs (взял, увидел) are in the past tense?

Russian does not shift tenses in reported speech or perception the way English does. After verbs like увидеть (to see) or сказать (to say), the subordinate clause keeps the exact tense that was true at the moment of the action. Since the speaker thought "I look older" right at that moment, выгляжу stays in the present tense.

Why use с собой instead of со мной for "with me"?

Собой is the instrumental form of the reflexive pronoun себя. In Russian, whenever a pronoun refers back to the subject of the clause (in this case, я), you must use the reflexive pronoun. Saying я взял со мной would sound unnatural to a native speaker.

Why is the verb выглядеть used here instead of смотреть for "look"?