Jess,
The fact is that no insurer will provide cover for a driver under 21 of age I'm afraid. So you will need to wait till your boyfriend reaches 21 before you can start looking for
short term car insurance, which is available from 1 to 28 days.
The shortest insurance term that your boyfriend can get is for 1 month cover. If you go to
eCar Pay As You Go Insurance, you will be able to get an insurance quote for a month. If the quote seems affordable, then you can purchase it straight away and he will be insured for his birthday, the weekend and a couple more weeks after which you can cancel the policy.
That's the best alternative that I can suggest.
