Unable to sort my photos

The "Sort > Keep sorted ..." is grayed out, because you are currently viewing the "Photos" view.

All predefined views created by Photos for you are having a fixed sort order. You cannot change the sorting. For the predefined albums and views the sorting is shown in gray, disabled, so you can see, what the predefined sort order is supposed to be.

If you create an album on your own, you can sort it more freely - it can be sorted by the title or the date, or manually, by dragging the photos around.

It is simply not possible to change the sorting for predefined albums at all. Create your own albums as Old Toad explained, and send a feature quest to Apple to provide more sort options (https://www.apple.com/feedback/photos.html).

I am using the scrollbars to allow quick access to the bottom of a predefined album. By default the scrollbars are hidden in Photos. I changed the System Preferences > General > Scrollbars, so the scroll bars will always be shown and clicking in the scrollbar will jump to the spot that is clicked. This has the added advantage, that all panels in Photos that can be scrolled, will show a scrollbar, and I can see, if a panel has hidden options, that can be revealed by scrolling.

1 - How can i arrange my current view in the "Photo" view arrange from the newest(at the top) to the oldest(at the bottom).

2 - Previously when the Photo library was created that was how my photos were arranged.

The "Photos" view is set by the application and can't be changed. However, you can create a smart album with the following criteria:

Of course all of your image files must have an extension for it to work.

Once you have the smart album you can sort it any way you'd like: