What about Lancel and Tyrek Lannister? Lancel is around 17 years of age and Tyrek is about 14 when Eddard and Robert arrive at KL in AGOT. Aegon would have been around 17 if he was still alive. Lancel as Aegon would be unlikely, even though his age is perfect, because I think it would have been hard to pull a fast one on Kevan.
Tyrek on the other hand is the son of Tygett, Tywin's and Kevan's deceased brother. If Tyrek was born before the rebellion, then there may be a case, but if he was born after, then there is no way for him to be Aegon. The real cause of my proposing Tyrek=Aegon is that Tyrek's disappearance has never been explained. He was not killed in the riot. He was not held for ransom. He has not appeared with Stannis, Renly, Doran, Littlefinger, Jon, nor Dany. So where is he?
One explanation is that Varys had Tyrek kidnapped in the confusion of the riot. Varys knows most everything... if Tyrek=Aegon, then Varys can hold him against Dany or use him in conjunction with Dany.
Also, Tyrek was conveniently married to an infant, Ermesande Hayford. This way he was kept from being married to a great house that might be hostile to a Targaryen return. But since he never consumated the marriage, Lady Hayford could always be set aside later.