Type is wrong. You made instance of SelectList here.
ViewBag.BikesResult = new SelectList(db.Bikes.Where(x => x.Sex.StartsWith(searchparameter.Sex) && x.MinAge < age && x.MaxAge > age), "Id", "Name");
But you tried converting to List <BikesProj.Models.Bike>.
@foreach (var bike in ViewBag.BikesResult as List <BikesProj.Models.Bike>)
{
<option>@bike.Name</option>
}
I am not sure becaouse I don't know about your SelectList class definition.
But I think that below code may help you.
@foreach (var bike in ViewBag.BikesResult as SelectList)
{
<option>@bike.Name</option>
}
If it doesn't work, please let me know your SelectList class definition.