c# - Linq To Entity does not support -

i learning mvc , storing user's date of birth show age. data saved properly. sort data followed this tutorial. works on first name , last name on sorting age throws exception only parameterless constructors , initializers supported in linq entities.
code action is

        public actionresult index(string sortorder, int? page, string currentfilter, string q)     {         viewbag.currentsort = sortorder;         viewbag.fnsortparam = string.isnullorwhitespace(sortorder) ? "fname_desc" : "";         viewbag.lnsortparam = sortorder == "lname" ? "ln_desc" : "lname";         viewbag.agesortparam = sortorder == "age" ? "age_desc" : "age";         var query = q;         if (query != null)             page = 1;         else             query = currentfilter;          var users = db.myappusers.select(a => a);          if (!string.isnullorwhitespace(query))         {             var nquery = query.toupper();             users = users.where(a => a.fname.toupper().contains(nquery) ||               a.lname.toupper().contains(nquery) || a.email.contains(nquery));         }         switch (sortorder)         {             case "fname_desc":                 users = users.orderbydescending(a => a.fname);                 break;             case "lname":                 users = users.orderby(a => a.lname);                 break;             case "ln_desc":                 users = users.orderbydescending(a => a.lname);                 break;             case "age":                 users = users.orderby(a => new datetime(datetime.now.subtract(a.dob).ticks));                 break;             case "age_desc":                 users = users.orderbydescending(a => new datetime(datetime.now.subtract(a.dob).ticks));                 break;             default:                 users = users.orderby(a => a.fname);                 break;         }     //            public datetime age     //{     //    { return new datetime(datetime.utcnow.subtract(dob).ticks); }     //}      int pagesize = 3;         int pagenumber = (page ?? 1);         return view(users.topagedlist(pagenumber, pagesize));     } 

and view is

    @foreach (var item in model) {     <tr>         <td>             @html.displayfor(modelitem => item.fname)         </td>         <td>             @html.displayfor(modelitem => item.lname)         </td>         <td>             @{                 var age = new datetime(datetime.utcnow.subtract(item.dob).ticks);                 @html.displaytextfor(modelitem => age.year)             }         </td>         <td>             @html.displayfor(modelitem => item.email)         </td>     </tr>                 } 

i can't figure out. can help?