Again the myth about age!!
And TS having smaller breasts than GG's
never been proven EVER.
A study in the netherland saw that TS after 2 years had breast significantly smaller than GG's, the problem with that is first, when your older you need bigger doses of estrogen to compensate for lower HGH levels and also because of those lower levels, for some, dosage cannot compensate and growth is slower, but still they're no reason on earth why eventually if dosage is high enough long enough it doesn't reach GG potential. Also, dosage tend to be prescribed uniformally instead of in response to growth rate (which would be indicative of responsiveness to hormones and human growth hormone levels). That coupled with conservative dosing means that many TS's get shortchanged in growth speed and even final results.
To be fair, a study of TS, should use appropriate dosage and be done after 10 years, not after 2 years.
Another problem, TS have an unrealistic view of what normal breast size is. After puberty, the average is 34B in the US, as a women grows older, she gains weight and it gets to 36C average (band size and breast size increases with weight gain, but this has nothing to do with the intrisic size of the growth potential, which is still 34B).
A 34B average with lower HGH could be reached in up to 10+ years if dosage are not kept up.
Often TS diminish their HRT dosage too soon because of doctor conservatism, just after SRS (No real reason, since dangers are very low compared to GG's). That leads to underdevelloped breasts.
Because of frame size, even if a TS has exactly the same breast size as if she'd started at puberty, they may look too small.
Previously progesterone was not used. Lately it gets used a lot more.
If appropriate dosage are used and your HGH levels are not so low that bosting estrogen can compensate to give results in reasonable time. Which is the case for most under 60, then you'll reach you growth potential.
This potential may be disapointing. But, some GG's also have very small breasts.
BTW, my syster's a 34B, and my mother and all my aunts never got over C when they were young. I'm at 34C in 14 months after losing 25 pounds, If not, I'd probably be 36C (which is bigger than what I got now, but i prefer being daintier, the way I'm going, I'll probably end up a 32D, not bigger than now, but with more projection).