Littles make wonderful ageplayers because someone who is naturally childlike can of course pull off the role of a child seamlessly.
I see that people often get confused by the two, or consider them the same thing.
I don't consider that the same thing in the slightest.
Age-play and DD/lg are similar, but also very different.
They work so well together if that's what you're after, and I think that's why people confuse the two so easily, as they sometimes seem to mesh into one another.
If you ask an age-player her/his age, then you will usually receive a concrete answer of the age they are playing.
Usually, a little won't snap in and out of their little mode straight away, it's a progression into it and a progression out of it.