Where did you get that username from?

[Stefl1504]

1504 - year of birth... uuum... date of birth^^

Stefl

-abreviation of an very old user name of mine: SteFlEx
-Stefan is my first name... and Stefl is a nickname for Stefan in my country^^... it is pronounced: Shteh-fl

you can choose for stefl but 1504 has only one option^^