I've been doing some date-calculations. Mahiette tells us that Pâquette 'la Chantefleurie' Guybertaut's daughter, Agnès, whom we know as Esméralda, was born on St Paula's day in 1466. St Paula, a pious Roman widow, has her Italian webpage here (this is a useful Italian site for checking up on saints' days and pics). She is commemorated on the anniversary of her death, 26 January. So when we meet her, she's just 3 weeks off her 16th birthday, and is 16 and a half by the time of her execution.
Since Quasimodo is named after the introit sung on the day of his adoption (Quasimodo, or Low, Sunday, the week after Easter Sunday: Quasi modo genite infantes, alleluia: rationabile, sine dolo lac concupiscite, alleluia, alleluia, alleluia. – "As newborn babes… desire milk reasonably, without guile"), this date, too, can be checked. In 1467, Easter fell on 29 March, so Claude adopted him on 5 April. The service is connected with newly-ordained priests, so that, too, would fit.