What changes can we expect in terms of processing speed and working memory capacity across the lifespan

It decreases with age.

Explanation:

Processing speed is described as a process that can directly affect "executive function yet not considered as an executive skill. Therefore, the "slow processing speed" tends to impact an individual's flexible thinking, working memory, attention skills, and planning & organizing.

The changes that an individual can expect associated with the working memory and processing speed capacity across someone's lifespan is that it decreases with his or her age. It could happen because an individual's losses his or her capabilities to ignore or avoid certain distractors. However, it has been noted that an old person takes more time to process something or encoding as compared to a younger person.