Emperor Jing used him during the rebellion of the 7 states.

But when Han Wudi was fighting against the xiongnu, he refuse to use Li Guang to fight the xiongnus and relied on wei qing and huo qubing instead.

Not saying that wei qing and huo qubing is lousy, in fact they were good generals. but I find it weird as to why Han Wudi did not want to use Li Guang too

Li Guang was a bit in over his head. He used to be competent, but he was getting on in the years, serving his third generation of emperor. He lost a few battles either due to bad luck or miscalculation ... or, as some say, politics.

In addition, Han Wu Di liked young men, and Li Guang was getting too old. Han Wu Di had no problems using his son (Li Gang 李敢) and grandson (Li Ling 李陵).

Old generals are good as they have experience what.

The han wudi show say that Han Wudi did not want to use Li Guang because he was good at defending but not good at attacking whereas Wei and Huo are good in attacking so Han Wudi use Wei and Huo instead.

I try to do a search but can't find any information with regards to whether this is true anot

Maybe and maybe not. I do know that Han Wudi was a bisexual (check out Shi Ji and looked at some of the stories about him) and greatly prefer handsome young men at his side. I think Li Guang had a disadvantage for being a lot older than Han Wudi at that time.

As a warrior, Li Guang had little to be criticised for. But as a general and a field commander, his track record was not favourable.

Perhaps it could have been misfortune that the Han army strength was not quite on par during the earlier campaigns against XiongNu. Several times, Li Guang found himself against numerically superior XiongNu forces and suffered badly. Nonetheless, he was also careless enough to lead his own troops to be trapped by the enemies in pursuit of fleeing foes.

In terms of character, he had 2 black marks against him. One was the mass execution of Qiang forces he persuaded to surrender. This was considered a major transgression at the time, an act against the Way of Heaven. Another was his spiteful execution of a junior officer who once offended him when taking Li Guang to task for violating a night curfew.

When examined objectively, using historical records, Li Guang was not as good a general as he could have been expected to be.

Nonetheless, the fact that he got lost during his last campaign was extremely puzzling. He was supposed to be an experienced general, and yet managed to get lost. Either he was really as impulsive/reckless as charged, or he was deliberately misled (as the commentator Bo Yang implied in his commentaries).