Lawyers and social workers said certain factors could be given more weight in offences relating to sex with minors. These could include distinguishing if the act was done by someone in a "position of trust".
They also suggested reviewing the conditions for statutory rape - having sex with a minor under 14 - which carries a harsher punishment than sexual penetration of a minor under 16.
The Attorney-General's Chambers' (AGC) statement yesterday said the public prosecutor will not appeal against the four-year jail sentence given to mixed martial arts instructor Joshua Robinson for having sex with two 15-year-old girls .
The AGC explained that the 39-year-old's charge of sexual penetration of a minor under 16, in which offenders may be jailed for up to 10 years with a fine, was the "most serious charge that the prosecution could have brought on the facts of this case".
Having sex with a minor under 14, with or without consent, is considered statutory rape. Offenders may be jailed for up to 20 years, with a fine or caning.
Key reasons for decision
• Securing a guilty plea would spare three young victims the trauma of testifying and being cross-examined at trial.
• Joshua Robinson did not commit "sexual assault" - two of his victims were aged above 14 when they had consensual sex.
• Victims consented to the sex acts, so he had not committed rape or outrage of modesty.
• Caning is not provided for offences that Robinson was charged with.
• Sentencing is broadly in line with precedents.
• The Attorney-General's Chambers does not differentiate between Singaporeans and non-Singaporeans in discharging duties.
Joshua Robinson's four-year sentence
The District Court ordered the sentences for the following charges to run consecutively:
• One charge of sexual penetration of minor: 24 months;
• One charge of making an obscene film: 12 months;
• The charge of possession of obscene films: six months;
• The charge of exhibiting obscene object to young person: six months.
Another 20 charges were taken into consideration. Total sentence: four years' jail.
Lawyer Amolat Singh, who has been practising criminal law for 25 years, said factors such as injuries sustained and whether drugs were used on the victim could have brought about a longer sentence in cases similar to Robinson's.
But there should also be tougher punishment if the offender is in a position of "trust and confidence", such as being a teacher.
He also suggested that the age limit of below 14 for statutory rape may be rather "arbitrary and artificial", adding that those aged from 14 to 16 should be equally protected.
"While (Robinson) should not be tried in a court of public opinion, the public's view is relevant to show outrage, and that something needs to be done," he said.
Another criminal lawyer, Mr Eugene Thuraisingam, asked whether the law should legislate for a large age disparity between the victim and offender. A large-enough age difference could result in a charge of statutory rape, even if the victim, a minor, was above 14, he suggested.
"But a balance has to be struck between a young man who makes a mistake, and an older man who preys on young victims. Perhaps, the law does not draw that distinction sufficiently," he said.
Ms Iris Lin, a senior social worker at Fei Yue Community Services, said the gap in knowledge of sexuality between 13- and 15-year-olds is not as large these days.
"Nowadays, children have access to a lot of information," she said, adding that the cut-off age for a harsher punishment is debatable. "But the law needs to draw a line somewhere," she conceded.