Well, yes and no would be the best answer to that question. Since, there is no definative way to prove one 'Hadith' is more accurate than another it's unsure as to the exact age of Aisha (Muhammads last wife.) Although, it's commonly accepted in the muslim community, and the greater international community that.
A) Aisha had atleast reached puberty.
B) The marriage wasn't consumated until there were signs of preparedness.
C) That Aisha was around the age of 12.
Now, considering it was legal for a 12 year old to marry in the United States and Britain in the early 20th century, it's not too surprising that in the 13th century, such a thing would happen. Infact, in many countries it's still legal for marriages at around that age. Also, the biological signs of preparedness is as good an indication as any that we can come up with, whether you can refute that scientifically or not is your decision.
Considering all of that, it's not that strange if Aisha really was in her early teens.
In modern society though, it's less common for something like that to occur. It's just a reflection of society, rather than anything else. Consider this, in 500 years lets say theoretically we have technology that allows us to reach the age of 200 years. People marrying and having a legal age of sex at 16, might seem to weird and abnormal too.
In regards to your question, it's probably true.
