My baby has a peanut allergy that I discovered on his first birthday. Who knows how long he had had it.
You can develop allergies at any time in your life. My daughter developed a severe allergy to cats when she was about 14 or 15. We had cats when she was little and never had any problems. Now if she is near them for even a few minutes, her throat closes up and she has trouble breathing, her eyes water and swell. Allergies can be deadly.