I thought acne started at adolescence, but my infant already has it. Is this normal?

Absolutely. Normal! it is called newborn acne, worst in boys than girls. Due to hormones passed on from the mother. Self limiting, will resolve on its own in a few werks'time. Not to worry then.
Yes. Baby acne appears as small, red or white bumps on the face, especially the cheeks and forehead. Acne may spread to the neck and upper chest. There is no specific treatment for this, as it should fade in a few weeks or months. Don't scrub the acne and don't put creams or lotions on it, as these can make the acne worse. If the acne seems severe to you or lasts past 3 months, call your doctor.
Yes. Babies can develop acne ("baby acne") starting at 3-6 weeks old. Luckily, it does not hurt or itch and resolves by itself around 2-3 months old. No special care needed.
Yes. Infant acne can be present at birth but usually appears after a few weeks of age. It also only last a few weeks. No treatment necessary.