Yes, a 20 year old man, if he is assessed as having 'normal' development and the context of his relationship with a 15 year old girl indicates an ongoing relationship that would not necessarily end when she reached the legal age of consent, will not need anything like the same level of treatment as a 20 year old who had coerced a 15 year old by pretending to her that they were boy/girlfriend. Using sadistic 'child pornography' (abusive images of offences against children) would be an aggravating factor indicating the need for extensive treatment. A sex offender who undergoes treatment and intermittent testing for effectiveness of the intervention has to demonstrate a 'treated profile' which means the risk of reoffending is satisfactorily lowered.
A 'normal' boyfriend who does not raise that level of concern would show a treated profile in a very short time, often by having one to one discussions with a psychologist or specialist worker in which he shows whether he has learned what the issues of concern are and can demonstrate he has a realistic and achievable plan to behave responsibly in future.