Plenty of hitters are late bloomers though. The recent Phillies playoff runs were build in part on Ryan Howard, Chase Utley, Shane Victorino and Jayson Werth, who had their first full ML seasons at ages 26, 26, 25 and 28, respectively. There's nothing wrong with not being established at 25.
Souza's minor league stats are ridiculous and the projections (like Steamer) support him being an average regular or better.