(posting this here so it doesn't clog up the other thread)
Emma was 16 when she was with Neal.
Henry's birthday cannot be in August because he was already 10 in October (on Emma's birthday) then in when he meets Neal (mid season 2) he was 11. Season 1 ends within a week or two of Valentine's Day and (I can't be certain as I haven't watched season 2 in a long while) lasts roughly a month, at most. So 2x14 had to have taken place around mid-late March, possibly early April at a real stretch, in 2012.
So he turned 11 March/April 2012, so was born March/April 2001. Emma would be 18 the following October. The working backwards, he was conceived in June/July 2000 (which makes sense as A&E said Emma and Neal were together "for a summer". She was 16, 17 that October.
Now on to the relationship. Nevermind the legalities for a second, there is a huge maturity difference between 16 and 23. He was an adult and she was a child (a homeless, love starved, slightly naive child at that). Frankly I find the idea of a man his twenties manipulating a child into a date, drinking with her and then planning to move in with and start a life with her quite repulsive (seriously watching that fake pregnancy scene and the motel scene with Emma's real age in mind..... ugh). She was not old or mature enough to either consent to sex (and I doubt she'd have ever had much sex ed to begin with given that she ran away from Ingrid when she was 13/14 and had likely been homeless all that time) or start a home and new life with him.
[think this says it all really]
In Oregon, where they were, the age of consent is 18. So it was illegal