It seems plausible, doesn't it? But it's incorrect. A girl's body is absolutely not the same as that of a post-menopausal woman.
Our bones reach peak density between the ages of about 25 and 30 and begin to very gradually decline from our 30s onwards.
Bones are constantly being replaced and replenished. Two types of cells within the body effect this replenishment. Osteoclasts break down the old or damaged bone (think of them coming along and eating holes in your bones). This clears the way for their partners, the osteoblasts, to come along and make new bone to fill in the gaps left behind.
After age 30 there begins a slight discrepancy between the two processes, so that slightly more bone is removed than is replaced.
During the years following menopause, with the sudden loss of hormones when periods cease, bone loss drastically increases. The osteoblasts cannot keep up with the osteoclasts, who seem to go into overdrive. The result is the development of a condition called osteoporosis, which makes the bones more likely to fracture.
One of the commonest areas to fracture easily is the spine. The vertebrae crush together - and deformity of the spine and displacement of the internal organs can result. Sometimes people are not aware that they've suffered vertebral fractures until they notice a loss of height or a change of body shape (e.g. hunched shoulders, belly sticking out) but usually the excruciating pain (which sometimes never goes away) makes it all too obvious that something catastrophic has happened.
The bodies of adult women depend on oestrogen for not only bone health but also cardio-vascular health. HRT goes a long way to protecting older women from declining health. It's about far more than just treating the immediate side effects of the menopause.
Please read up on it and make an informed decision. Your older self may be be very glad that you did.