Activity

The “experience of redness” implies awareness of redness.  Thus it requires not only perception of things that are red, but conscious awareness of some kind that one is seeing “red”.    That involves behaviors such as discriminating red, recognizing that it is “red”, and perhaps thinking or feeling (and being aware of the feeling) something from seeing the color.

Some of those behaviors are not available to a fully functional infant human being.  They are developed over time, particularly as complex verbal behavior is developed.  So by 4 yrs of age, I would guess that most humans would have learned to not only see red, but to identify it and be aware of it and think about it (or as you would say, experience redness).