You've already had this question answered. If that website really said that, then they are talking crap.
Gynaecomastia is not cancer.
Gynaecomastia is very common in adolescent boys.
No adolescent boy has ever been diagnosed with breast cancer. The youngest man, by any years, ever diagnosed with breast cancer was 24. His case made news internationally.
Breast cancer is almost unheard of in women under 25, is extremely rare in women unde 30 (fewer than 0.1% of those diagnosde) and very rare in women under 40.
Men make up fewer than 1% of all those diagnosed with breast cancer. Most men diagnosed with breast cancer are over 60.
No teenage male has ever been diagnosed with breast cancer
I suggest that if you're going to read about breast cancer on the internet you do it on reputable and reliable breast cancer sites:
http://www.breastcancer.org
http://www.breastcancercare.org.uk
http://breakthrough.org.uk/
Do a searchfor 'male' and 'gynaecomastia' (gynecomastia on the first one as it's American). And take notice of what they tell you.
EDIT: forgot to mention - even in women over 50, most breast lumps are not cancerous; over 80% of breast lumps considered suspicious enough for biopsy are found to be benign. And pain is in fact rarely a sign of breast cancer; most people diagnosed with breast cancer have felt no pain.