I'm not a native speaker...
Me too :)
Even if he was a young man at the begins of his professional career, he showed from the start high proficiency, take-charge capability, creativity, persuasive ability and self-confidence on high profile international working events.
Though he is quite young in his profession he displays maturity in his proficiency, self-confidence, accountability, especially athigh profile international working events.Well.... I really don't understand what you mean by "high profile international working events". What do you actually mean by this?
Dr. Mario Rossi is also a terrificenthusiastic team player with a deep understanding of collaboration and work division key roles, been conscious of his competences and his position, he always place the common interest upon the personal achievement.
... take the later part to a new sentence :)