hai hall  i  wrote a code but it throws an error

public class inlinewrapper {
    public string startdate{set;get;}
    public opportunity  opps{set;get;}
   

}



public class inappps {
    public list<opportunity>apps{set;get;}
    public inlinewrapper linewrapper{set;get;}
    public decimal yeargap{set;get;}
    public inappps(){
        
        apps=[select id, name,CreatedDate ,closedate from opportunity];
         for(opportunity os:apps){
        linewrapper=new inlinewrapper();
        linewrapper.startdate= string.valueof(os.CreatedDate);
        linewrapper.opps=os;
  
             
        }
    
            
        }
       public void caluclation( ){
             linewrapper=new inlinewrapper();
           datetime dt1= datetime.valueof(linewrapper.startdate);
           date convertation=date.newinstance(dT1.year(), dT1.month(), dT1.day());
           date close=linewrapper.opps.closedate;
            yeargap=(convertation.monthsBetween(close));
           
}
}

<apex:page controller="inappps" docType="html-5.0">
    <apex:form >
        <apex:pageblock >
        <apex:pageblockbuttons location="top">
            <apex:commandbutton value="show" action="{!caluclation}"/>
            </apex:pageblockbuttons>
         <apex:pageblocktable value="{!linewrapper}" var="s">
        <apex:column >
          Date: <apex:inputText value="{!s.startdate}" size="10" id="demo" onfocus="DatePicker.pickDate(false, this ,true);" />  
             </apex:column>  
             <apex:column headerValue="closedate">
                 <apex:outputfield value="{!s.opps.closedate}">
                     <apex:inlineeditsupport event="ondblclick"/>
                 </apex:outputfield>
             </apex:column>
            </apex:pageblocktable>
            {!yeargap}
        </apex:pageblock>
    </apex:form>
</apex:page>