For Provident Fund there is no retirement age and therefore, as suggested by Rohit, you can put the entire 12% of employer's share to the provident fund account along with employee's share of 12% without bifurcating it as 8.33% to Pension Fund and the remaining 3.67% in Provident Fund.
Regarding payment of Gratuity, if gratuity is not paid at the time of retirement, you can add on the service to the continuing service. In such case, whenever he leaves and gratuity becomes due the service will be counted from his initial day of service.
In practical companies make employees retire at the age of superannuation fixed, ie, in your case 58 and settle their gratuity and thereafter issue fresh appointment order on fixed term contract basis renewable every year.
Regards,
Madhu.T.K