Is it possible to have had symptoms of narcolepsy in your 20's?

Yes. Typical age to first develop symptoms is teens and twenties but it can occur earlier and later.
Absolutely. Narcolepsy actually has 2 peak times of onset: in the mid-teen years and in the 20's. Unfortunately, there is often a delay of up to 10 years between onset of symptoms and diagnosis. If you have excessive daytime sleepiness, sleep paralysis, vivid dreams or nightmares, or brief spells in which you lose muscle tone, please see your doctor and tell them your concerns.