Is the Nikon D200 good enough for A Level Photography?

I know it's old now but it's in my price range and also my dads old AI lenses will fit it

I don't see why not. The most important part is the manual control, and you certainly have that.

I'm sure it will be perfectly fine!

If it works then it's perfectly good for A-levels and even Degree studies, and there are many pro photographers who still have models like the D200 and D70/90 as their spare bodies.

In some ways it's better than a newer model as it's now worth so little that you need have few qualms about using it in riskier situations or in a way which might leave the odd scratch on it, and where other photographers fear to take their gear is often where the best shots are.

Later models have larger LCD screens and higher megapixel counts and a few other non-essential bells and whistles but with a decent lens even a 2MP camera will produce good A4 sized prints and yours has more than enough at 10.2MP so you can crop images comfortably without noticing a loss of detail.

Using that model with those older non-AF lenses will not only teach you how to use a camera but will force you to slow down to compose and manually focus on exactly what you're shooting. It also means that when you have some money of your own you can start adding good modern AF lenses so you'll be able to build a collection of very good glass; upgrading the body could be expensive (less so if you go for good used examples) and won't have any real effect on your image quality.

It's more than enough.

To my mind - good enough and more.

Sure, as long as you take the time to learn how to use it.