Was Crocodile stronger at Marineford? Or was he holding back in Alabasta?

 During the Alabasta arc, Crocodile displayed a level of power that was initially considered overwhelming by the Straw Hat Pirates. He possessed the Logia-type Devil Fruit called the Suna Suna no Mi (Sand-Sand Fruit), which granted him the ability to control and transform into sand. He had a reputation as a Shichibukai and controlled the desert kingdom of Alabasta from the shadows. His strength was showcased through his battles with Luffy and others. At Marineford, Crocodile was present as part of the war that took place at Marine Headquarters. While he did participate in the battle, he didn't display the same level of dominance as some other powerful characters present. This has led fans to speculate that he might not have been as strong as initially portrayed in Alabasta. It's important to note that power scaling and character abilities can be subject to interpretation and development by the author. Oda often keeps details deliberately open-ended to keep the story intriguing.

Gandalf says that the Balrog is "older than he can reckon." How old is the Balrog, exactly?

 The Balrog is a fictional creature from J.R.R. Tolkien's Middle-earth fantasy universe, and as such, it is not possible to determine its exact age. In the story, the Balrog is described as a being of great power and ancient origins that has survived from the First Age, a time before the events of the story take place.

In the novel The Lord of the Rings, Gandalf the Grey, a powerful wizard, encounters the Balrog during a battle in the underground realm of Moria. When Gandalf faces off against the Balrog, he states that the creature is "older than he can reckon," suggesting that its age is beyond his ability to determine.

The Balrog is one of the Maiar, a class of powerful spiritual beings that were created by the godlike being known as Eru Il├║vatar. It is not specified exactly how old the Balrog is, but it is clear that it predates the events of the story and has survived from a time long before the beginning of recorded history.