Can a syphiis sore appear 18 months later on a penis even if i wore a condom?

No. But if you're concerned about syphilis, you an have a blood test. The most common cause of penile ulcers or sores is genital herpes; you might have longstanding herpes, even if this is the first time you've noticed anything. Get seen ASAP: accurate diagnosis depends on testing very soon after onset. Good luck.

Not in primary syphilis as a solitary lesion after 18 months. If worried pl get tested