User blog comment:Romerox/How many years will be calculated for each of the characters/@comment-67.54.224.77-20101129030120

One of the reasons that Phineas and Ferb are step brothers is becuse Dan and Swampy wanted them to be the same age and also in the episode were Phineas and Ferb went 20 years in the future to get and metel and wood fusing tool Linda says that her Phineas and Ferb are 30 years old so that makes Phineas Ferb 10.