Jack in the Green: How old is he?

With May having gone through a full swing of seasons in one month I would like to look at one of the quintessential May characters in British folklore. It appears that Jack in the Green maybe one of the youngest. It seems that with the upsurge in popularity of the old figure of the Green Man & Robin Hood characters he has been lumped in with them. It isn't until the 18th Century that he is depicted & not until 19th Century when the term Jack in the Green was first named in writing. So here is my theory, the Jack in the Green came out of some over posturing of garland making which was popular in 16th-17th Centuries or as a piece of art imitating life with depictions in both written & drawn form could have been greatly exagerated & people took it at face value & it somehow ran away with itself & in this case quite literally so. I somehow get the feeling it may be a bit of both. So old maybe but not ancient. But why do we seem to put group all foresty type beings in one great lump, why can't Robin Hood, the woodwose, Green Man, Jack in the Green, the Holly King, the Green Knight etc be seen as a different being by some of the fluffy or New Age lot. Before you know it the Jolly Green Giant will be the next thing added into it & I'm not entirely sure what a sweetcorn logo would have to do with the other characters. I like my May customs & different folkloric characters, but that is because they are different. In Britain we don't have the gods of many other countries so please don't deminish our folk characters too.