User blog comment:PlantyThePottedPlant/Random Topic Blogging III: Blog Harder/@comment-3006892-20130512072002/@comment-4123215-20130513014458

Well, I would figure since Phineas's voice is getting deeper, yet still high pitched, I would say he's 13.

Ferb is taller, more calm (Usually), and has a deeper voice than Phineas, so I believe Ferb is 14.

This takes place during the same summer that the show started on (They could have done multiple things in 1 day), so Candace is still 15.

Linda doesn't show many signs of aging aside from occasional minor faults, so I'm gonna say she's 43.

Lawrence seems younger than Linda, but they seem of similar age in the flashbacks, so I'll say 41.

Stacy would probably be 15, same as Candace.

Isabella I'd say is 12, though possibly leaning on 13.

Buford has a deeper voice than the other kids, and is pretty tall, so I'm gonna guess 14.

Baljeet I would say is 12, since he definitely acts more immature than the rest.

Irving is probably 13, though he may be 12, I'm not sure.

Heinz used to date Linda if I'm not mistaken, and they seemed of similar age, so I'm going to say 44. (Though some sources say 47, and in that case, I'm far off and need to catch up on my P&F)

Perry is 12, since he was around since Phineas was a kid.

Jeremy is 16, most likely.

Suzy is... 8, maybe?

I probably forgot a lot of characters, but oh well.

Finally, due to his shape and posture, I assume Pyro (From Team Fortress 2) is a guy, though I wouldn't be surprised if it's a girl.