I feel it depends on the lines. Certain lines you'll see bone growth for longer than from other lines.
I have a girl who grew more bone until close to 2.5 years in age. I never saw that prior but heard 1 of the lines fairly heavy within her pedigree grows bone for longer than most other lines. I feel her first litter also helped at a bit over age 2, once all of her clearance were back and she came into season.
I'm pleased with how she turned out yet worried between age 1 and 2 unneccesarily.
I don't know if there is an average age when bone growth subsides. I've seen different ages with different Labs, my own and others.