The US tech giant announced on Monday that it is buying D'Aloisio's news-condensing mobile app Summly for an undisclosed figure reported to be around £20 million ($30 million) -- making the London schoolboy one of the youngest self-made multi-millionaires on the planet.
D'Aloisio dreamed up Summly while revising for a history exam when he was 15 -- but two years later he speaks of market share and intellectual property with the self-assurance of a CEO three times his age.
"Yahoo! is one of these classic, well-known Internet companies," he told AFP in an interview at the office of his London publicist, sprawled in a chair in maroon jeans and a t-shirt.
The tousle-haired teen hopes the Yahoo! deal will see the technology behind Summly -- whose financial backers have included US actor Ashton Kutcher and Japanese artist Yoko Ono -- reach an audience of "hundreds of millions of potential users".
D'Aloisio's journey to tech super-stardom began at the age of "nine or ten" when his parents, a lawyer and a banker, bought him his first laptop.
He taught himself how to video edit and before long moved on to programming -- spending school holidays building apps at his home in leafy Wimbledon, south London, as "a hobby".
He launched his first iPhone app, a "workout for fingers" called Finger Mill, when he was 12. Others followed, including music app SongStumblr and Facemood, which attempted to predict a user's mood based on their Facebook status updates.
The big breakthrough came in 2011 when D'Aloisio launched Summly's forerunner Trimit, which cut down long web articles to tweet-length summaries.
The app received positive reviews from several tech blogs and quickly racked up tens of thousands of downloads.
Then, out of the blue, the teenager was contacted by representatives of Asia's richest man -- Hong Kong billionaire Li Ka-shing.
"They cold-emailed me," said D'Aloisio.
Li was the first investor to contact him and, not knowing what to do, the teenager ignored the message.
Two days later he was "stunned" when Li's people approached him again, and this time D'Aloisio agreed to a phone call.
"They didn't know I was a 15-year-old, so I had to explain that," he said with a smile.
"It was frightening. It was a hobby, I didn't expect this to happen. But at the same time, I had nothing to lose -- I was a 15-year-old."
Li invested $300,000 in Trimit. D'Aloisio used the cash to develop the algorithm the app used to identify the key topics in a news article, working with scientists at Stanford University among others.
Summly officially launched in November last year, on D'Aloisio's 17th birthday -- and the rest is history.
D'Aloisio will take up a job in Yahoo!'s London office in the next few weeks.
"I'll be integrating the Summly technology into different areas we feel are appropriate for Yahoo!, and more broadly helping them with their mobile product design," he told AFP.
He insisted that he will continue to live at home, resisting temptation to splash out on a teen bachelor pad.
His parents are "very enthusiastic" about his success, he said -- but are keen to keep their son's feet on the ground.
"I still get in trouble if I don't have my room tidy," he said.
The family celebrated the Yahoo! deal by going out for dinner.
As for buying himself a present with his multi-million pound windfall, it will be limited to "a bag or shoes or something".
"It's not going to be anything wild," he added. "I can't even buy a car because I don't have a licence yet."
As D'Aloisio starts work at Yahoo!, most of his friends -- who he says are "psyched" about the Summly sale -- will be finishing their A-Level exams before heading off to university.
D'Aloisio, meanwhile will begin studying for his A-Levels "outside office hours", and would love to read philosophy at Oxford University some day.
As for his long-term plans, nothing is set in stone -- a point emphasised by the large question-mark printed on his t-shirt.
"Long-term I do want to do other companies," he said, adding that he was interested in working with artificial intelligence.
"We'll see what happens."