Do I need ATPL(A) to fly Cessna 525?

No, to fly as a pilot-in-command on Cessna C525 Citation you do not need to have an airline transport pilot license - ATPL(A).

The reason is that the fact that the Cessna C525 Citation aircraft is from a certification point of view a single-pilot aircraft high performance complex aeroplane operated in multi-pilot operations. The EASA Type Ratings and License endorsement list, the Cessna C525 Citation recognises as a single-pilot aircraft.