From the USA. First things first: regardless of the answer to your question the most important thing is for you to recognize your courage, persistence, hope, and perspective in asking the question. These uncomfortable thoughts, your struggle with them, your detailed understanding of what is and isn’t happening to you, are significant strengths being used in coping with it all. I admire your ability in facing this issue so directly.
There are several overlapping pieces of information and I’d like to sort them through for clarity.
The first is a distinction between being a pedophile and Pedophilia OCD, or POCD. The POCD is when there are unwanted harmful or sexual thoughts about children. What is important about this differential diagnosis is that with POCD there is no desire to harm a child, but the intrusive thought plague the sufferer. The result is often panic, anguish, shame and depression. In other words, the intrusive thoughts are repulsive and not something the person wants to act on.
Pedophilia is termed pedophilic disorder in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5.) To be classified as a pedophile according to the DSM you would need to be at least 16 years old, at least five years older than the child, and the sexual urges and fantasies have either been acted on or caused actual interpersonal difficulty or severe distress because of the intense, recurring urges. The International Classification of Diseases (ICD-11) “… a sustained, focused, and intense pattern of sexual arousal—as manifested by persistent sexual thoughts, fantasies, urges, or behaviours—involving pre-pubertal children. In addition, in order for Pedophilic Disorder to be diagnosed, the individual must have acted on these thoughts, fantasies or urges or be markedly distressed by them. This diagnosis does not apply to sexual behaviours among pre- or post-pubertal children with peers who are close in age.”
I am elaborating on the definitions because typically acting on the thoughts or severe stress surrounding those specific thoughts are part of the diagnostic profile from either the DSM or the ICD-11. For more information please read here.
You’ve not acted on your thoughts with children and they frighten and disgust you. More than this, you have purposefully engaged in different thoughts to test their effect. If you have the power to change your thinking to be reflective (“I check my groin to see what I am feeling, I am paranoid I might have sex with underage girls…) it means you have some degree of understanding and control over them. This is the most important thing about what you’ve said. You are experimenting and to some degree controlling these thoughts to test them out. This implies that Cognitive-Behavioral Therapy (CBT) may be a very effective treatment for OCD intrusive thoughts as it aims to give you control over them, which you already appear to have at some level. You can learn more about this and other styles of therapy here.
While I can’t offer a diagnosis I can offer my encouragement is to find a therapist very familiar with OCD who uses CBT for its treatment. The find help tab at the top of the page can help you locate someone in your area.
Your ability to reflect on your own thoughts combined with your above mentioned strengths are good indications that with the right therapist these unwanted, intrusive thoughts can be effectively dealt with.