The Montblanc 146 is one of the icons in the world of fountain pens, with a long history running from a start of production in 1950 through to the present (with a small break during the 1960s). In that time, the design of the pen has changed, however, this means that estimating a production date for a particular pen can be fun (depending on how you define “fun”).
This page has a good overview of which features correspond to which years.
This particular pen has a mono-tone 14K gold nib, which immediately puts it in the range of 1975 to 1990. The light-blue “solid” ink windows (seen in the photo below) were made until 1979.
This means that this pen was made sometime between 1975 and 1979, which corresponds to a comment made by the person from whom I bought it, who said she’d owned it since the 1970’s and it’s been sitting in a drawer for about 45 years…
Total weight: 22.4 g
Body weight: 14.0 g
Total length (not posted): 124.3 mm
Total length(with cap): 142.8 mm
Barrel max diameter: 12.9 mm
Cap max diameter: 15.3 mm (across band)