Best age is relative, most people do it at about 4 months old. Do have to age for about 1-2 days, and meat will be tougher, and more flavorful, that store bought chicken. Not as much meat either but that's normal.
It takes a few hours of incubation before an embryo starts to grow, and about 40 hours of incubation before you can crack open and egg and see it with the naked eye. Most can't see the embryo that is cracked open till about 60 hours of incubation, as that's when the blood starts to become apparent. The embryo will start looking like a visable embryo to the naked eye at about 3-4 days.
It takes a few hours of incubation before an embryo starts to grow, and about 40 hours of incubation before you can crack open and egg and see it with the naked eye. Most can't see the embryo that is cracked open till about 60 hours of incubation, as that's when the blood starts to become apparent. The embryo will start looking like a visable embryo to the naked eye at about 3-4 days.