How do I tell the age of a bamboo stalk?

Bamboo is supposed to be strongest when it's around 3 years old. But I can't find any instructions on how to tell how old a culm of bamboo is.

I'm making a bamboo bike.

lemonie7 years ago
Jayefuu lemonie7 years ago
+1. That article was a good read.
Re-design7 years ago
Here's a good article.  Look down about 1/4 of the way down under "using bamboo".