This is called Sinhamu in Nepal. Essentially they are powder/paste containers used in worship and/or rituals.
The book Artistic heritage of Nepal, by the Handicraft Association of Nepal, mentions these are used ‘during Guhya puja (secret pujas) and other karmakanda rites performed according to Vajrayana rites’. At the end of rituals/puja, the powder from Sinhamu is received by the participants to be applied to the forehead. These containers are meant to be used along with the divine mirror. An example of the divine mirror is on this site.
Here the two containers, one with a lid, are supported by separate turtle bases which in turn are placed on a common rectangular base.
The scales on the turtle, the beading on the base of the containers and the rims of the lid, the lotus petal pattern on the side of the rectangular base, the foliage design at the bottommost level and patterned legs supporting the platform indicate the importance attached to this piece. A great example Newari artistic talent.
This bronze is about 14.5 cm in height and the rectangular base is 11cm by 5.5 cm.
I do not have any estimate of the age.