Albus would be in his third year when young Lily starts at Hogwarts -- she's nine during the epilogue, and they say that she has "two more years" before she can go. As for young James, he would be anywhere from his fourth and above. It isn't directly specified that he's only a year above Albus, but that is more likely (and if that's the case, he'd be in his fourth year when young Lily starts). However, it is also possible that he could be older -- fifth year or so.
And in terms of Cho, Murray is right, and a more specific answer would be anywhere from September of 1978 to August of 1979, as those in Harry's year could have been born anywhere from September of 1979 (like Hermione) to August of 1980.
~Megan
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