[Top-SecreT]

ich würds so in etwa versuchen

datetime oldest;

for(int i = 0; i < OrdersTotal(); i++){
    if(OrderSelect(i, SELECT_BY_POS)==true){
        if(!oldest || (OrderOpenTime() < oldest)){
            oldest = OrderOpenTime();
        }
    }
}

for(int i = 0; i < OrdersTotal(); i++){
    if(OrderSelect(i, SELECT_BY_POS)==true){
        if(OrderOpenTime() == oldest){
            OrderClose(...);
        }
    }
}