Welcome to Flyertalk YOUNGMML, and welcome to the BA board. It's good to see you here, and hopefully you will find this a useful and interesting resource.

And yes, unfortunately as soon as you leave Gold - which is the end of the month after the membership year - then with it you lose seating rights and other benefits. It works the other way too, if you booked something as Silver then became Gold then you can move to exit rows and first row in First and shorthaul (and for that a telephone call is sometimes needed). You are not the first person to come across this either.

You will be able to pay for exit row seats at 14 days before travel, and select them for free at T-3 days and / or OLCI.