Okay so I have a lose idea of what is going on, I will just dish it all out now then explain things later on. Bullet pointing will make it easier. - Set in present times, maybe a little in the future. - Revolves around a hidden society of Witches that blend easily with normal society. - Imagine gossip girl with magic. - Set in London - Main character is a boy called Nathaniel Astor, he was cursed to remain with a 15 year old body, he's now 19. I have a few characters, im struggling to think of a suitable villain though. Any more info or anything please just ask
That isn't a plot. It isn't even a storyline. You need to do a lot more before you're ready to ask for help, to put it bluntly. Please read this thread about What is Plot Creation and Development?. It will at least give you a starting point.
You've got the setting, now you need the conflict. Your hero wants something (what and why?), and has to struggle to get it. What is preventing him getting it? What are the consequences if he doesn't get it? Who is the villain, what does he want and what does he do about it? Who is the victim? What is the time factor? Every good plot should have a ticking clock somewhere. And of course, what can you do to make things even worse for your hero?
best thing i can suggest (works for me, dunno about everyone else) get the main story settings and ask yourself, who what where when why and how for each point. - Set in present times, maybe a little in the future.... (this world or alternate?) - Revolves around a hidden society of Witches that blend easily with normal society.... (who are the members, good or evil society. does it include warlocks) - Imagine gossip girl with magic. (ignore this for now, characters and dialogue will help show this as a style over the whole story) - Set in London. (is it part of plot or can it be any major city, even a made up one) - Main character is a boy called Nathaniel Astor, he was cursed to remain with a 15 year old body, he's now 19. (why was he cursed, who cursed him. is he seeking revenge, a cure or both.. have you thought about making him older. 15 to 19 isn't much of a leap.) I have a few characters, im struggling to think of a suitable villain though. (did the villan curse him, is he / she a member of society or their enemy?) don't know if that helps, but just something i thought of quickly.
Are the witches good or evil, and how old are they? (or, how do they seem?) And, why has the boy been cursed? You'll need to decide about these issues in particular before you hammer out the plot. Which, as has been pointed out, does not exist at present.
