Kaidan was born in 2151 into a family already familiar with space: his father served in the Alliance military. After his mother was downwind of a transport crash in Singapore, Kaidan was exposed in utero to element zero and beat the odds, gaining biotic potential instead of terminal brain cancer. At the time little was known about human biotics, but when the possibilities became better understood, a company called Conatix Industries was set up to track accidental eezo exposures. Children who showed enough potential to be worth augmenting with implants were 'encouraged' to attend BAaT (Biotic Acclimation and Temperance Training) which was conducted at Gagarin Station and nicknamed 'Brain Camp' by its attendees.
Source: Mass Effect Wikia, "Kaiden Alenko," available under the CC-BY-SA License.