First, there are gals that start HRT later in life and still get good development. Age, genetics, hormone regimen, nutrition and body type all play a part in physical development. I started at 60 and now have a 38C/40B depending on bra brand.
There are some high-end silicone forms with thin edges that are makeup compatible. Most have self-adhesive that works well inside of a bra. If you want to go braless, you'll probably need silicone adhesive to keep them in place. Telesis 8 is one of the best. Blending the edges with makeup to create a seamless transition is a difficult art to master.
TBH, if I were still wearing forms and wanted realistic cleavage, I'd buy a high quality breast plate. Cleavage is a given since it's one piece. Going braless is a snap. No adhesive is needed. The edge can be hidden with a neckless or choker. The biggest downside is they tend to be hot.