How long should wait for my goosebery to mature?

Not really, the gooseberries don't interest the birds as much as other fruit, but they say Whitsun was the time to start thinning the gooseberries, for the first tart! (Six weeks after Easter) you find if you thin some of the bigger ones to take the weight off the branches especially if you have a good crop then the others will fill as the plant has less to feed, they may be short of water if they are not filling, we have had a very dry two months in our part of the country, I don't know about you, our rain has been light when it comes.

Cover your fruit bushes with netting, water the roots well.