There is no real evidence of May’s age and we assume she’s in the same age as Coulson but I don’t think so anymore. I think she’s younger and here’s why - in the beginning of their flashback we could see Phil’s rank from that time, he was level 4. Then we could see Melinda’s rank, she was level 3. Then they were talking about their academies, acadeMIES so we know that they didn’t graduate together so it’s possible that Melinda is younger and she graduated later. Also, despite the fact that May is probably not so keen on getting better ranks, she wouldn’t be level 3 if they graduated together - she’s good at what she does and so is he, I don’t think he’d be able to outrank her, though.