The specified type member is not supported in LINQ to Entities. Only initializers, entity members, and entity navigation properties are supported

You cannot use properties that are not mapped to a database column in a Where expression. You must build the expression based on mapped properties, like:

var date = DateTime.Now.AddYears(-from);
result = result.Where(p => date >= p.DOB);
// you don't need `AsQueryable()` here because result is an `IQueryable` anyway

As a replacement for your not mapped Age property you can extract this expression into a static method like so:

public class clsProfileDate
{
    // ...
    public DateTime DOB { get; set; } // property mapped to DB table column

    public static Expression<Func<clsProfileDate, bool>> IsOlderThan(int age)
    {
        var date = DateTime.Now.AddYears(-age);
        return p => date >= p.DOB;
    }
}

And then use it this way:

result = result.Where(clsProfileDate.IsOlderThan(from));

A lot of people are going to say this is a bad answer because it is not best practice but you can also convert it to a List before your where.

result = result.ToList().Where(p => date >= p.DOB);

Slauma's answer is better, but this would work as well. This cost more because ToList() will execute the Query against the database and move the results into memory.

You will also get this error message when you accidentally forget to define a setter for a property. For example:

public class Building
{
    public string Description { get; }
}

var query = 
    from building in context.Buildings
    select new
    {
        Desc = building.Description
    };
int count = query.ToList();

The call to ToList will give the same error message. This one is a very subtle error and very hard to detect.