We've been writing, recording and performing live shows together for 13 years. People may think you're old, but your genre is a lot more forgiving of age than most others. People may think you're doing something wrong to have been around that long without making any money.
Quality is king in the music business.
I know very successful writers who have under 25 songs. That's not to say that they don't write a lot because they write all the time. They know when to keep something though and when to throw an idea back for another day or ditch it all together. Don't deny how long you've been around, but don't mention it unless you're asked. The skills you've learned over the last 13 years are all people care about and they don't need any more details than that.