I was engrossed in the Philip Roth novel The Plot Against America on the train from New York when a gray-haired woman leaned across the aisle and said, "That's quite an advanced book you're reading, young lady."

I smiled and said, "I'm 21."

The woman apologized. She'd thought I couldn't have been more than 16.

I've always looked young for my age. When I was in fourth grade, I burst into tears at Hair Cuttery when the stylist asked if I was in kindergarten. That's quite an insult to someone who's an "upper-classman" in elementary school.

I'm just over five feet. In my grade at Bethesda's Westbrook Elementary School, there was only one girl shorter than I was. Every year, I hoped she'd be in my class so I wouldn't have to sit in the first seat of the first row in the class picture. By high school, she had six inches on me.

It's not just my size; plenty of petite people look their age. I've been told time and time again that I have a "young face." I guess that's a euphemism for "baby face." Fortunately, people tell me that the minute I start talking, they realize I must be older.

My sister is 2H years younger, but for a while she's been taller, and people who don't know us assume she's the older sister. She calls me her "little big sister."

I helped her move into her freshman dorm at college last fall. I'm confident that if I'd dressed like an incoming freshman, in that "trying to look cool but not like I'm trying too hard" way, I could have passed for one. But I had worn clothing for the activity of the day: hauling boxes up the stairs in the August heat.

In athletic shorts and a tank top, my hair in a messy ponytail, I was asked, "What grade are you going into?" by every parent and freshman who came by.

I like to swim at the YMCA when I'm home in the summer. On more than one occasion this year, teenage lifeguards asked me to exit the water for adult swim. When I told them my age--the minimum for adult swim is 18--they blushed and apologized.

My 21st birthday was anticlimactic, as I celebrated it while studying in Rome, where kids start drinking wine around the time they start eating solid food. When I came home, I got to use my over-21 driver's license for the first time.

I took a weekend trip with friends to Atlantic City and had my first gambling experience. The blackjack dealer scrutinized my ID for what seemed like five minutes and then told me I looked like his 14-year-old niece.

At a bar mitzvah I attended recently, a guest asked the hostess to fix me up with her 13-year-old son. I had thought I looked particularly mature that night in a cocktail dress, heels, and makeup. I guess 13-year-olds dress pretty precociously these days.

At least I haven't been given a children's menu at a restaurant in a while. This once happened in high school when I was out to dinner with a boyfriend.

My mother says the same things used to happen to her. She stands an even five feet, almost a full inch shorter than I do.

Once, she and my father--well into their twenties and married--were on an airplane. The flight attendant offered my dad Time and Newsweek. She asked my mom if she'd like Ranger Rick.

Now Mom tells me she'd be thrilled if someone mistook her for a 30-year-old. I'll keep that in mind next time I'm carded for a PG-13 movie.

Sara Levine (sblevine@sas.upenn.edu), a former editorial intern from Chevy Chase, is a senior at the University of Pennsylvania.