Aria-, I currently do the job you want. I know what the job entails and I have a pretty reasonable idea as to who our owners are and what they expect to see in their crew. I haven't flown with any one younger than 27.
I have only met 1 person in my 42 years that was mature beyond her years when she was 19. She already held a CPL and had already been working as a commercial pilot.
There's nothing stopping you what so ever for applying but, please don't be surprised if they (Netjets Europe) suggest you get some life experience before reapplying. I wish you well and good luck.