Preprocessing since age 13
I implemented my first ever PHP app at 13 on now-defunct AndrewTaylor.EU. Great fun when it was discovered by someone in class and it went "viral" amongst 25 students.
Things have scaled a bit since! My biggest PHP success story was building an app for my college at Durham University to manage the hyper competitive signups for £2.50 formal dinners with waiter service. My web app (UCFormal) serves the whole college of about 1,000 students and has 600 monthly active users. In its first term, my software handled over £6,000 in billing, produced 1,428 barcoded event tickets, authenticated 7,000 logins and processed 3,000 direct messages on its messaging system. Managing so much data has been a massive challenge and greatly taught me about security, scalability and stakeholder management with software engineering.
Another success story was UCWelfare - a highly anonymous messaging app I built for the welfare team at my old Durham college. It allows students to seek anonymous advice for a wide variety of issues, such as stress, anxiety, depression, bereavement and heartbreaks.