No u are not to small I play flank for my high school girls team yes I know u are a guy but I an only 136cm and 54kg and I have no trouble tackling or clearing people that are twice my size our of a ruck so no u have 24kg and 44cm on me so I think u would be fine to play flank on a guys team at your age if u can run fast go for a center but u are kinda big to play canter
Just from those stats you gave you're almost already good to play. But what position you're going to play depends on the rest of your team. If they're as big or bigger than you then you have a chance at center. if not, then maybe as a forward
gustav, what is light and short about 78kgs and 180cm at the age of 16 years? If I had been 78kgs and 180cm at the age of 16 I'd have been thrilled to play flank, eighth man, or even lock. When you are eighteen you might be 188cm which is a good height for a flank. If you keep on growing you might see 192cm by the time you are twenty. That is a beneficial height for an eighth man at senior level.
Go play rugby its a sport for all different sizes of people like me I'm 6'4" and 288lbs and 14
I think you'll be alright , if your quick maybe go center , as Long as your tough and have good fitness you'll be fine