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I think this varies a lot, Rosie. To have a conscience requires empathy, and it seems from recent studies ("Zero Degrees of Empathy" by Simon Baron Cohen or see U-tube clip of same title and author) that the endowment of empathy is at least in part genetically heritable.
A person with no empathy (excluding Aspergers) feels no remorse for causing pain or harm and hence acts without a conscience. At the zero degrees end of the spectrum are the sociopaths who can be capable of serious crimes.
At the opposite end are people of such extreme empathy that they care too much and can damage themselves in the process.
In between are most of us, who have some degree of choice, who can choose to work hard at becoming better people or who are gifted at finding it easy to care without going overboard.
I believe a big part of conscience is socially conditioned from the cradle, learned by how our parents and others around us treat us, and also from societal mores.
We are, after all, born helpless and knowing nothing. Our instincts are less compelling than those of animals. This gives us more flexibility, adaptability and choice. Most of us are able to learn lessons from our mistakes.
From what I have seen so far, many people do become more considerate, conscientious, responsible and understanding as they mature emotionally - so yes - I think ethical awareness can and does grow throughout life, possibly for most people.
