Looking to build a road/tri bike for the daughter.  She is 13 yo, 4'10" inseam 28" weighs about 70 lbs.  Her measurements put her into the 46/47 cm frame size.  Interested in the BXT Pro 1.0 because it is di2 and direct mount brake ready.  The smallest frame size is 49, so I think it will allow her to grow into it.  Don't think she is going to be any taller than 5'.

I don't know much about BB so would appreciate the help.  Looking at BSA or PF30.  Leaning towards a threaded BSA for maintenance ease.

This is the link
https://www.aliexpress.com/item/2017-Chinese-carbon-frames-super-light-Aero-Design-carbon-road-frame-49-52-54-56cm-China/32761635885.html