No it's not. I hope you like math, because this involves chance.
There are over 7 billion people on this planet. A normal year has 365 days, but once every 4 years there is an extra day. However, if the year can be divided by 100 that extra day is dropped and if the year can be divided by 400 the drop of that day doesn't take place, thus it still has that extra day. This means the last drop of that day happened 116 years ago, but people rarely reach that age. So that means that bit of information is useless and we can work with an average of 365.25 days a year. If you got that, we can go over to the second part.
Since you're born in March, you weren't born on that extra day. This means we can calculate the number of birthdays on one day as is. Take the over seven billion and divide it by 365.25 and you'll see that there would be over 19.1 million people with the same day of birth, given that each day would have an equal number of births and not taking the effect of daylight savings time into the equation.
Now to look at the age. Very young people can't make an account here and probably have a very slim chance of finding this website, and older people often don't use internet that much either. This makes it very hard to guess how big the chance was your day of birth would be either the same or one day apart, so let's leave that out.
So if you met someone on this site with the same age as you, there would be a chance of 3/365.25 that that person being born on the same day or it being only one day off. That's a chance of about 0.82% for one random person of the same age. Admitted, it's not very likely, but definitely possible. Besides, if the group of people that are the same age gets bigger, the chance of finding one (or more!) people with the same birthday goes up.
tl;dr: Read paragraph above. Thanks for coming to the forum btw, it was a long time ago since I had this much fun with maths.