Masturbation/Why does this happen?
Is it true that the older a guy gets the more he has to depend on using visual aids for masturbation? If so, is it because a guy's libido gets weaker with age?
I don't think it's true. However, you might be right that more males use visual aids as they get older. I will check my survey results on that point and get back to you.
I have checked the results of a survey I did in the first half of 2007. According to this survey, males start out masturbating more than once a day and then fall into an average of 6-7 times per week by age 18. The first time the average falls below six times a week is age 29. Males are still masturbating at least five times a week, on average, until age 42, and then at least 4 1/2 times a week until age 49. This doesn't take into account any sexual intercourse they are having.
In terms of total sexual output (masturbation + intercourse), males peak in the late 20s. and maintain at least 7 orgasms per week on average until age 42 and at least 5 orgasms per week on average until age 57. This says that if a male's libido gets weaker, it gets weaker very slowly, over a period of many decades.
Meanwhile, when it comes to using visual aids while masturbating, the same survey finds that a majority of males are using them most of the time they masturbate as early as age 11. Two thirds of males use pictures most of the time before they're out of their teens. Picture use does not continue to go up as libido (as measured by sexual output) goes down. If anything, they are part of the same process.
Therefore, it is false that declining libido is a cause of using visual aids to masturbate. The increase in visual aids happens while the libido is increasing.