As far as I know, airsoft is legal for 18-and-overs.
Full-auto guns certainly are allowed.
The really tricky bit however, is that importing a full-scale replica airsoft gun is prohibited and will likely result in seizure. There are workarounds, but they usually entail greater risk or expense. The same applies for certain airsoft gun components like the receiver.
Here's a link to a page that will tell you all you need to know about importing:
The short of it is that it will probably be more troublesome to import prohibited items than it would be to buy from retailers which may already have the item in the country.
I may be a bit of a noob, but I suppose the best advice I can give is to browse all of the stickied topics on the forum and let the information gradually sink in.
Senior members, feel free to correct me if I'm wrong, or expand on my post. Or denounce me for being an ignoramus and a ponce.