Background: Alexander Bell was born in Edinburgh, Scotland, on March 3, 1847. The family home was at 16 South Charlotte Street, and has a stone inscription marking it as Alexander Graham Bell's birthplace. He had two brothers: Melville James Bell (1845-70) and Edward Charles Bell (1848-67), both of whom would die of tuberculosis. His father was Professor Alexander Melville Bell, a phonetician, and his mother was Eliza Grace (nee Symonds).
Context: As a child, young Bell displayed a natural curiosity about his world, resulting in gathering botanical specimens as well as experimenting even at an early age. His best friend was Ben Herdman, a neighbour whose family operated a flour mill, the scene of many forays. Young Bell asked what needed to be done at the mill. He was told wheat had to be dehusked through a laborious process and at the age of 12, Bell built a homemade device that combined rotating paddles with sets of nail brushes, creating a simple dehusking machine that was put into operation and used steadily for a number of years. In return, Ben's father John Herdman gave both boys the run of a small workshop in which to "invent".  From his early years, Bell showed a sensitive nature and a talent for art, poetry, and music that was encouraged by his mother. With no formal training, he mastered the piano and became the family's pianist. Despite being normally quiet and introspective, he revelled in mimicry and "voice tricks" akin to ventriloquism that continually entertained family guests during their occasional visits. Bell was also deeply affected by his mother's gradual deafness (she began to lose her hearing when he was 12), and learned a manual finger language so he could sit at her side and tap out silently the conversations swirling around the family parlour. He also developed a technique of speaking in clear, modulated tones directly into his mother's forehead wherein she would hear him with reasonable clarity. Bell's preoccupation with his mother's deafness led him to study acoustics.  His family was long associated with the teaching of elocution: his grandfather, Alexander Bell, in London, his uncle in Dublin, and his father, in Edinburgh, were all elocutionists. His father published a variety of works on the subject, several of which are still well known, especially his The Standard Elocutionist (1860), which appeared in Edinburgh in 1868. The Standard Elocutionist appeared in 168 British editions and sold over a quarter of a million copies in the United States alone. In this treatise, his father explains his methods of how to instruct deaf-mutes (as they were then known) to articulate words and read other people's lip movements to decipher meaning. Bell's father taught him and his brothers not only to write Visible Speech but to identify any symbol and its accompanying sound. Bell became so proficient that he became a part of his father's public demonstrations and astounded audiences with his abilities. He could decipher Visible Speech representing virtually every language, including Latin, Scottish Gaelic, and even Sanskrit, accurately reciting written tracts without any prior knowledge of their pronunciation.
Question: How old was he when he invented the dehusking machine?. Whats the answer?
at the age of 12, Bell built a homemade device that combined rotating paddles with sets of nail brushes,