Thomas Brodie-Sangster was 20 in Phineas and Ferb: The Movie: Across the 2nd Dimension when he played the character 'Ferb Fletcher (voice)'.
That was over 13 years ago in 2011.
Today he is 33, and has starred in 39 movies in total, 19 of those since Phineas and Ferb: The Movie: Across the 2nd Dimension was released.
In Phineas and Ferb: The Movie: Across the 2nd Dimension, I think Thomas Brodie-Sangster looks: