Here is a link to a number of suggestions I have compiled for hardening of firmware.
I'm pretty sure that a lot can be said about the list, so please post coding tips or links to pages with good information of software hardening.
iapetus.neab.net/.../hardening.html
Per; I have no idea about average ages but I'll bet that Erik and myself severely skew the curve age wise. Still I enjoy the info on this forum. Al Bradford