Thanks, that is a lot to think about.
First, you are perfectly correct about asking for scientific evidence. One thing I am trying to do at the moment is to pin down exactly what the evidence is for statements on both sides of the argument. Breast health is heavily weighted with mythology, and it is amazing how certain statements get repeated over and over without any primary source being identified. There is also an apalling lack of research in this area, despite the £1 billion retail sales in the UK annually.
My statement was based on other sources. In truth we have very little data on what provides support or lack of support to the breast. Recently emphasis has been shifting from the ligaments to the skin, pregnancy has an obvious effect on skin elasticity. The breast contains largely fatty tissue, and therefore has little anchorage for its mass, so any breast other than the smallest would be expected to point down rather than out. I think people discussing gravity confuse a natural 'lie' to any lengthening of the breast, which may be seen in some women with multiple pregnancies and breast feeding.
There is a natural loss of elasticity in all tissues with time as you say, most notably in the skin. Therefore there definitely is an age effect.
When I look back at my original statement, I can see there is some ambiguity. I was not trying to suggest that gravity pulls the breast down. Only that a breast without support will naturally lie against the chest wall due to gravity, in the upright position.
The arguments for bras weakening breasts is based on observations from other parts of the body, in particular immobilising limbs, not on direct observation.
So yes, basically I agree with you.