The amino acids you get from natural foods that have NOT been altered by someone in a lab are fine. And by altering, I mean removing the natural complex amino acids and replacing them with man-made concoctions, such as the phenylalanine is aspartame. Here, the manufacturers have created a completely man-made molecule of phenylalanine, aspartic acid, and methanol - hence, aspartame. This is NOT found in nature.
Spirulina is wonderful when kept natural, and the better products will keep it in its natural form. This means the amino acids in it, phenylalanine is one of them, are in a natural balance and the body processes this "naturally."
So, this is a good supplement to use for anyone at any age. It will cause no harm, and the benefits to the body are numerous. And yes, Davidcam12, the "Super Food" products can contain spirulina, but some products are strictly the sea nutrients. Just check your labels to select the product you think is best for your needs.