We count how many days you have been alive and go the same number of days back before your birth. That is your mirror date.
Whoever was born on your mirror date was exactly your age today on the day you were born — your time twin. It moves one day back every day.
Your birth date stays in your browser. The people come from Wikidata, photos from Wikimedia Commons with their authors.
Only your browser remembers your date. We never send it anywhere.