Your case is likely to attract legal complications. First of all, knowing that he will not complete five years on his superannuation you should not have included gratuity as part of CTC. Secondly, if he was given full and final settlement you should have paid him gratuity proportionate to his service without reference to Payment of Gratuity Act but with reference to his appointment order which specifically said that he is entitled to gratuity.
Now, since his reappointment has been made for the benefit of the company ( there is every reason to believe that his continuing in service is badly required otherwise the company would not have employed him after his attaining the age of superannuation) you should consider paying him gratuity when he leaves the organisation provided the total service at the time of leaving including his past service is five years or more.
If you deny him the gratuity saying that his new appointment starts in 2010 only, the payment can be withheld. But, as stated, if he raises an industrial dispute, there is every chance that he may get it. This is because legally he has been in continuous service though you have changed the status of employment from 'regular' to 'fixed term contract' and that change will be treated only as a paper adjustment for the sake of employer about which the role of employee is absolutely nil. Now a days the authorities are very keenly watching on this aspect and directions are being issued in favour of employees. However, the legal verdict may take its own time.
Regards,
Madhu.T.K