Littlejohn
Short-term or temporary Car Insurance is available but is expensive when compared with annual policies. You can get quotes online for short-term policies. Do a search.
Get different quotes based on your age now and at your birthday by adjusting the details you enter when getting the comparison quotes. I doubt 2/3 weeks will make much difference. My experience of age related loading of premiums, is that the loading is gradually reduced over many years. Premiums do not suddenly reduce when you reach a certain age. Also age is only one of many factors taken into account when calculating the net premium.
Huckster