Well, you did say "several millions", so that would be more like 2000 lines. And depending on the environment, I'm aware of many people who do much less (not of their own volition or choice), so I have little faith in a long-term average being this high. I'll have to take a look that what Capers Jones wrote on this...
Also, 40 years? 1000000/40/52 ~> You're assuming the average developer writes 500 lines of code per week? That seems absurdly slow.