My grandma had alszheimers. I'm 26 and I seem to be more forgetful than my peers. Are there any tests for me to take to determine the cause?

Alzheimers unlikely. Common causes of impaired memory in young people include brain injury, drug/alcohol use, seizure disorder, sleep apnea/deprivation. You're too young for alzheimers. You could also be perfectly normal. Psychologists can administer careful memory tests to say whether your memory is normal, and if not, how it is not. You may want to run this by your primary care doc first, though: testing is $$.
Not really. Have you had any memory testing done by a psychologist to confirm your impression of forgetfulness? If confirmed, there are many more plausible explanations than alzheimer's at your age such as depression, anxiety, adhd, drug use, alcohol use, med se's, accidents/head injury/concussions. Etc. If really concerned, see your doc who can run lab tests to rule out other explanations.