While death is a consequence (not punishment) of our sin, we will all have to face that consequence - disease in and of itself is not a punishment. Terminal illnesses are not just something that's happened in our time, terminal illnesses (such as cancer) have been around since the beginning of human-kind.
If AIDS is a punishment then so is getting hit by a car when you run a red light. For some it's a natural consequence and for others (like babies who get AIDS) it's one of those unfair things that happen, like cancer. Illness doesn't just pick on those that Christianity dubs 'sinners'.
Beyond that, we have no idea how long HIV/AIDS has been around. Most people who die of AIDS actually die of a complications related to AIDS, like pneumonia. AIDS was discovered in the 80's - it didn't just suddenly appear in the 80's, it was discovered. it's probably been there for a long time before that.