Publicis Groupe is a 100 year old company founded by, a then 20yo, Marcel Blanchet. Started his own radio station, introduced the legendary Édith Piaf to the world and built Publicis into the largest advertising company in the world they've only had 3 CEOs in the last 100 years!
An agency founded by a 20 year-old has been acquiring Adtech companies left right and centre. They've spent $3bn+ on buying Influential ($500m), Captiv8 ($150m), BR Media Group and most recently LiveRamp ($2bn).