Hi Krista
The timeline is important in the sense that it's preferable to start taking HRt within 10 years of menopause or aged under 60 because this is generally accepted as the "window of opportunity" for maximum benefit and least harm. However this also depends on your general health and the type of HRT you take.
Although as CLKD says, brisk exercise is excellent for keeping healthy and including bones - this alone will not prevent bone deterioration (bone loss) which occurs when oestrogen levels drop after menopause. The extent to which this can be harmful will depend also on other factors like genetics, diet, longevity and whether you take HRT etc.
Bone health will always be improved by taking HRT, although not everyone will suffer from osteoporosis (for reasons given above) but if you live to 90 and go through menopause at 50 then that's 40 years without (so much) oestrogen so any additional years you take it are likely to be of benefit.
You are within the right timeframe for starting hRT ( again) ie well under 60 and only 6 years post meno so no worries there. Even after this time many women successfully start HRT and transdermal ( ie gels and patches) are recommended as beinbg associated with lower risk (if there is going to be any) - notably cardio-vascular/stroke.
You can mitigate any risks - as CLKD says - through healthy lifestyle, diet, increased exercise, reducing alcohol, body weight, etc so if you are generally healthy in these respects then also no need to worry so much.
I'm mid 60s and started HRT at just under age 54, always transdermal....I also take testosterone prescribed my GP (though initially through a consultant 6 years ago)
Hurdity x