What other "symptoms" does your son have, nikos? If he only has slightly unusual but improving social skills, then it might be worth watching how it goes over the next six months. But if he has obsessions, peculiarities in his motor skills, or other unusual features that are often linked with AS, then it might be worth asking to look further, if you're up for it at this stage.
My son is clearly intelligent - is only just 4 but can already read with expression, is very good with numbers and simple maths, has an excellent memory and concentration. He also has an excellent imagination and sense of humour and plays beautifully with his little brother. His oddities are: he was very delayed with his gross motor skills, because he is hypotonic and hypermobile, but also because he appeared to need to be taught how to crawl, etc, before he could attempt it for himself. He also has numerous motor tics already (eg pulling up his trousers all the time when completely unnecessary, lifting his eyebrows, making a noise through his nose). And, of course, whilst he gets on beautifully with his little brother, he isn't interested in socialising with other children. He is eager to please all adults, however, so his pre-school teachers all love him. He can also be rather obsessional - eg he loves listening to the same CD of 50 nursery rhymes all the time (sometimes quite happily just watching the CD player to see the number of the song) and he loves singing all 50 songs, in order. He can be distracted from this to do more interesting things, but will always hark back to it at some point.
There is clearly something unusual about my son, and I am still in a quandary as to whether to pursue a diagnosis now or wait until I see how he gets on in reception. Like your son, his social skills and other oddities (apart from the tics, which are getting worse) are improving all the time, but I am acutely aware that hypotonia, hypermobility, motor tics and obsessions are all frequently associated with aspergers syndrome (even if not, except for the obsessions, part of the diagnosis), so do worry. Besides which, of course, motor tics and poor sporting ability aren't exactly a recipe for a bully-free school life.