User blog comment:Mobo85/Questions for Aliki Grafft/@comment-4343598-20110909223747/@comment-68.189.187.161-20110912212040

We may see Ferb's birthday eventually, but as it stands it's almost certainly the case that Phineas is slightly older than Ferb, unless the potential Ferb birthday episode somehow takes place before Phineas'. We'd need confirmation for that, though, so it may be a question worth asking.