Tell a calf's age by heart girth

[jode]

Is there any way to guesstimate the age of a calf based on body structure? I thought our calf was about 3 months old on 11/24/07 (back when we first got her) but I have read some stuff lately that has me wondering if that is correct. Any links for info? The calf is question is reported to be a Brown Swiss, but even that part is not for sure.

We're trying to plan for when we need to start getting her ready for AI.