If you are going to let children get into romantic relationships(which I am not opposed to if the child has matured early) then that means they should be able to make their own choices about life just like adults and those choices include whether they have sex or not.
The question here becomes, Why are we opposed to pedophilia exactly? Is it because children are not mature? Well, Then why do we let 18 year old immature girls do what they want?
Is it because sex would hurt children? Well, If the child has matured, Isn't it their own choice to hurt themselves? People smoke knowing that is harms them. But no one cares about that for some reason.
The important thing is that we need to realise why we actually consider pedophilia wrong and take action according to that. We have to be careful though, As this is a slippery slope if we accept pedophilic actions.
My question is why are we tolerating pedophilia to begin with? We have people asking whether or not it's ok for a child to be in a romantic relationship with a possible sex offender. Of course not! Who's going to regulate the pedophile's relationship? Who's not going to speak out for fear of being labeled a pedophobe? Seriously, If we let these disgusting people get in relationships with our children, There's going to be a lot of pain down the road.
The key question here is what exactly is meant by a "romantic relationship"? If it involves sex or intense sexual activity then i think it is right this is banned. There could be an argument to be had about what the correct age of consent should be but that is a totally different debate.
If by romantic relationship we simply just mean what i would term affectioinate relationships ie giving and recieveing gifts (though not ridiculously expenisve ones or over the top ones), "dates", Hugs perhaps the odd kiss then i guess that providing the young person is ok with it then it could be something that might be acceptable. Although i doubt these are illegal anyway in most countries?