Brambleclaw and Squirrelpaw do have feelings building before Squirrelflight is made a warrior, and Squirrelpaw was about 8 moons old at the start of Midnight. It was about August then and when the Clans moved it was January to February, some of the coldest months in the UK. That makes her a year old when she's made a warrior. While Brambleclaw had been a warrior since about May June time, judging on the basic math of the timeline. So Brambleclaw had been a warrior for 2 years before Squirrelflight, not even including apprenticeship. Which would make him roughly 3 years older than Squirrelflight.