There can be a few reasons for the buttons to be disabled:
- As you can see on the reputation page, you need at least 5000 reputation points to approve or reject tag wikis, which also show up on the suggested edits.
- Besides tag wikis, your own edit suggestions you made will also show up in the queue. Obviously you can't approve or reject your own edit suggestions.
- You exceed the number of 30 votes a day
- You exceed the number of 5 votes on a specific user's edits a day
I guess the queue is just the same for every user and it isn't filtered on whether you can actually approve or reject it. The same goes for the flag page when you reach 10.000 reputation, you can see your own flags but basically they're just queued there, waiting for moderator attention.