choosing a young or old position

To select a position that is young in time, use:
bool SelectLastPosition()
{
   datetime time_last = 0;
  
   for (int i=PositionsTotal()-1; i>=0; i--)
      if (iposition.SelectByIndex(i))
         if (iposition.Symbol() == isymbol.Name() && iposition.Magic() == Magic)
            if(iposition.Time()>time_last)
            {
               time_last = iposition.Time();
            }
        
   for (int i=PositionsTotal()-1; i>=0; i--)
      if (iposition.SelectByIndex(i))
         if (iposition.Symbol() == isymbol.Name() && iposition.Magic() == Magic)
            if(iposition.Time()==time_last)
            {
               return(true);
            }
        
   return(false);
} by the way, look at pliz, what can be improved in it.
i tried to use the same f-y to select the oldest position, just changing the condition to:
if(iposition.Time() but since initially we set the time to zero datetime time_last = 0, then you will not find anything less than this time, i tried to assign the value 999999999999999, but it does not work, which value is better to assign?