I don't recall any episode talking about Lance's age. His is calculated by out-of-episode information and matching it as best as is possible with episode events. (Namely using the guidebooks, the second of which covers events up through season six and has Krolia's page say "About 19 Earth years ago, she crashed on Earth yadda yadda".)
I'm assuming the confusion is coming from Keith's trip through the Quantum Abyss? Keith and Krolia aged two years ahead of the rest of the cast because they entered the Quantum Abyss which is full of intense gravitational pull. I put it this way for other people:
"I'm no science expert, but essentially: the greater the gravitational force, the slower time flows, because gravitational forces warp the fabric of space-time. If a clock is dropped into a black hole, it would appear to move slower since black holes have unfathomable amounts of gravitational power; if you were falling with the clock, everything would appear normal, due to time being relative. [en.wikipedia.org/wiki/Time_dilation] The abyss is full of extreme gravitational forces affecting space-time because of the high concentration of super dense stars/massive celestial bodies found there. [See also here: businessinsider.com/do-astronauts-age-slower-than-people-on-earth-2015-8].
This is why time slowed down for Keith and Krolia and they experienced two years' worth of time (probably according to the clock in their space suit computers), while it didn't seem very long at all for the rest of the team (like a week or something), because Keith and Krolia were in an area of warped space-time and the rest of the team weren't."