Back in the early 1600s, dates weren't always put on coins. Instead, a system of mintmarks were used to indicate the approximate time a coin was issued. The mintmarks on your coin are located here:

The pics aren't quite clear enough for me to tell what the mintmark is. If I had to guess, I wouild guess "triangle". The mintmarks should be the same on both sides. Possible options for Class 4 sixpences like this are:
Mint under Royal control:tun (a barrel-shape) - 1636-1638
anchor - 1638-1639
triangle - 1639-1640
triangle-in-circle - 1641-1643
Mint under Parliament control but still striking Royal types:(P) - 1643-1644
(R) - 1644-1645
eye - 1645
sun - 1645-1646
sceptre - 1645-1648
So if my guess at the mintmark is correct, that would make it dated to 1639-1640.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis