That is never true! Dogs are not born badly behaved, it is the way they are treated and handled by people around them that shapes their personality. If “bad behaviour” is not corrected or the dog is not given any direction in life, this behaviour gets amplified with time.
All dogs big and small, young and old, male or female are train-able! We have personally trained dogs from 3 months old to 8 years old! What matters is identifying the problematic behaviour and having the will and patience to change it. Also, it is not just dogs who need training but the humans around them as well!