Adama "Cylons don't age! I knew you when you had hair!"
Salty "Well I'm a different kind of Cylon, one that we've never seen before."
That accounts for the final 5.
Meanwhile we saw considerably younger versions of some of the first 7 in the Razor Flashbacks.
Of course if they could accelerate to actual light speed immediately, and not a decent fraction of light speed slowly... The trip from Earth to Colony space would "seem" to take seconds, but that's not taking into account kinetic strikes on the ship, from hitting two thousand years worth of space dust and space pebbles all at once during those couple seconds, that it would be sane if they would stop now and then to make sure that they're not going to plough into anything like a planet or nebula either... Or alternatively plot a super weird course that takes them off the galactic plane mostly.