Size will be about 3"+ but some wont breed till about 4". Not sure one age it depends how they have been brought up. Eggs talk 3-4 days to hatch and another that long to absorb there yolk sacs.
Some plecos are very difficult to breed! Not true of bristlenoses, which are very easy to sex (males have lots and lots of bristles; females have few or none). As long as you have both sexes and a cave they will breed very happily in the average tank.