Why would someone you're dating lie about their age by one year?

Was it intentional? I have mistakenly said I was a year younger, many times

I've screwed up my age before when I didn't take the time to do the math

Maybe they forgot?

Maybe they're only 17... maybe they're only 20...

Maybe they wanted to seem younger, maybe they wanted to seem older.

Maybe they're bad at math.

Nah, I wouldn't be dating someone bad at math

Maybe they're just rounding the number up or down depending on how close it is to their birthday.

Maybe didn’t remember their age at the moment. Sometimes I’m off by a year

Maybe they forgot their current age because they recently had a birthday

Lie about just one year. Sounds odd maybe 6 or 9 years but just 1

Insecurity

I don't know but it's just the start of their series of lies

I always lie in order to attract the most demanding of catfish

How old are they? If they are underage….