The sentence "I took too long in the shower" is grammatically correct. In this sentence, "long" is an adjective. Adjectives are used to describe or provide more information about nouns or pronouns. In this case, "long" is describing the duration of time (how much time) the person spent in the shower. The word "long" is not a noun in this sentence. Nouns are words that name people, places, things, or ideas.
