26. Three pioneers - Burov, Gridnev, and Klimenko, named Kolya, Petya, and Grisha, arrived at the pioneer camp. It is known that: 1) Burov is not Kolya; 2) the brother of Burov's mother has the surname Serov; 3) Petya started school at the age of seven, always studied well, and this year will begin studying algebra and geometry; 4) Petya's grandfather - Semyon Mokrousov - works as a gardener at this pioneer camp and is very happy about his grandson's arrival; 5) Gridnev and Grisha are each one year older than Petya. Determine the name and age of each pioneer.
26. Burov - Grisha, he is 13 years old. Gridnev - Kolya, he is 13 years old. Klymenko Petya, he is 12 years old.