Hey. I find the easiest response to this is just to be totally cool and aloof about it all.
When they ask you your age indirectly, just ignore the question. They usually forget they asked you, and life goes on. If they get to know you for long enough and never actually 'ask', they'll eventually not care.
However, if they come right out and ask bluntly, dodging it just seems sketchy. They can tell you're embarrassed about it for some reason. So when they ask directly, don't even pause... just say, '37' with a straight face and keep talking. At this point they're totally lost... they're backpedaling trying to figure out whether they tooootally called it wrong, or you're BSing them. Eventually they stop you, back up, and say, 'No really... how old are you?'
You just keep chuckling and teasing them... 'What - just because I shave you don't think I'm 42?' HB: 'You just said 37...' You: 'I know. What's your point? Anyway... about them Red Sox...'
Haha. Finally you quit playing this stupid game and just be like, 'Haha - I'm 20. Calm down

I'm not some old creeper'. By now she's so 'not in control' that you could say you're 16. You've already established your control over the situation.