koreanfestivals1-7, Exercise 2: Hwangap

Model answer:

Why 60: it marks the completion of the sexagenary cycle of sixty, after which a second lifetime is said to begin. It is reached at international age 60 (Korean age 61).
Why before the birthday: the date is chosen to avoid inauspicious days, and the article says it is held before, not after, the actual birthday.

Reasons for declining weight (any two): longer life expectancy; some parents do not expect a ceremony and weigh later ones such as the gohui (70th) higher; fewer elderly people live with their children; larger ceremonies are more typical in rural than urban areas.
Hedging words: "reportedly", "possibly" (and "some"). They show that no figure is given behind the claims.

Sources: Wikipedia, Hwangap.