Try calling the Red Cross and asking them about that. Also some places may limit the age of the donor. Call around.
Unfortunately you can't.
Well, not in my country, for health reason and I'd assume most countries would be the same.
The same goes for is you're pregnant etc.
Generally they won't accept blood if you've had a tattoo done in the past 12 months as they don't rule out the possibilty that you could have contracted blood diseases whilst having your tattoo done.
You can always call your local blood donation centre and ask them :)