Letters, Numbers, and Colors…when Do Toddlers “Get It?”?

I have a 19 month old daughter who I think is average, developmentally, with most toddlers her age. She was slower with gross motor activities like crawling and walking, but like a lot of girls was quick to gain expressive language skills. Although she isn't always clear with words and babbles a lot, she does know all of the primary colors, many capital and some lower case letters, and most numbers up to 10. Is that normal for her age? She is very interested in letters and is constantly naming them on signs and in books, so maybe this is why? Just curious...I didn't know when they developed that sort of knowledge?