I was born this way. I'm bad at saying "l"s making them sound like "n"s and also "w"s like "r"s or vice versa. I have pronounciation problems. When I was younger I was brought to a teacher and she said she needs to help me with my sounds. But it was only 1 class and it didn't continue.
Also, in elementary school, this happened. They wanted me to practice with my sounds :P
I tried it but I still didn't get it :P
I TRY to roll it and it sounds weird :P but I'm sure people can figure out if I'm saying pero or perro.