"Ascending" to the next tech age always requires a certain number of current age techs. It helps prevent tech spamming.
BTW, I noticed a bug where Alterian was always #1 in Tech Victory ranks, forcing me to out tech them. It turns out, they were pathetically behind me. The Tech Victory ranking lied terribly. Dont know how repeatable this is, but if you doubt your tech victory ranking, start a diplo session with the enemy and compare techs just to be sure.
In my case, I had ALL of the age of ascension techs, and was about to finish building the ascension gate for the the win. Alterian was still rank #1 for Tech Victory, and I thought it was gonna be a nail biter. Turns out Alterian didnt have ANY age of ascension techs. I had 114 techs they didnt have, and they had only 15 techs that I didnt have. dont let this ruin your game, go back to killing them softly 