He was rescued by someone. He tells Neo that there was someone born in the Matrix, who could control it, reshape it as he saw fit (basically someone like Neo (this fits into what the Architect said about repopulating Zion every new iteration of the Matrix.))
Morpheus specifically says: "It was he who freed the first of us." Whether that implies that he himself was freed by this prior 'One', or afterward, I'll leave that up to you, but I personally think that he was 'freed' by other Zion-ists, not the prior-'One.'
I don't think it was the previous "One" who released him. Why? If that was the case, Morpheus would know there was another "One" and wouldn't consider Neo the "One." Because there's two...he'd call Neo the "Second" or something.
__________________
"You hear that Mr. Anderson? That is the sound of inevitability."
How old would Morpheus have to be to have been freed by the original one..
Well.. this is the seventh iteration of the matrix...
The one, is allowed to choose.. 16 women. and 7 men,, i believe... so look at the population now.. how many years must pass for the populationof zion to have grown that much..many hundreds.. anyone care to do the math ??
The war itself is only 100 years.. not the age of each Matrix iteration.
The population of zion isn't governed strictly by how fast the original inhabitants can reproduce sexually...there are the people they free too...and it doesn't take extremely long to get up to 250000 people that way. 2^14 times 23 is more than 300000 and that's a rather low estimate for how fast the 23 can free minds and reproduce but its still only 14 generations...I'd say zion can be repopulated pretty quickly.