How old is Billy from 'Stranger Things'?

This image appears in the gallery:
How old are the 'Stranger Things' cast and characters in real life?

1. 
2. 
3. 
4. 
5. 
6. 
7. 
8. 
9. 

10. 14 images

See the full gallery: How old are the 'Stranger Things' cast and characters in real life?