18 year old son

Hi everyone! My 18 year old son experienced his first seizure 8 weeks ago. Saw a neurologist and had an MRI and EEG. One week ago he experienced another seizure right before his appointment to see what the test results were. His MRI was negative,thank The Lord! His EEG showed slight abnormality in the left temporal lobe affecting,according to neuro,only a few cells. Neuro said this is something that could have been present since birth. My son has always been a perfect picture of health. I would love some helpful insight from others. He is taking Keppra as his treatment. I am an over worried mother and just wonder why,after 18 years this is showing up now.