Climbing hills is not the only way to become better at climbing. If you think about it physically, the difference between a hill and a flat is that you are riding at an angle so that the force of the gravity does not cancel out by the normal force of the ground. To emulate this on a flat, you'd have to have a spring attached to your bike pulling you backward while you're riding forward or have a strong headwind. Absent that, you can also emulate a hill by a far simpler method - high gear on a flat. Thus, to become a better climber, you need to always have quality workouts and ride as fast as you can for as long as you can. If after your ride you're not in pain, you didn't do it right. When I first started a few months ago, I tried so hard to keep up with the group that after every ride I would go home in agony and be in bed all day, out of whack. But I quickly advanced from last to top 1-3 on the hills and I have never done any hill repeats. So just put in the effort no matter what you're doing.

Let's also not forget the body weight. If you make serious effort, you will lose weight which will be one of the most important aids on your climb. Training alone might not be enough to get in perfect shape, so you also need to watch what you eat. If you want this badly enough, you can do it. Anyone can. But most people, most cyclists, do not. This is why you see old and young cyclists who have been in the sport for many years but are still overweight.

A few people already mentioned here - do NOT concentrate on hill repeats now. You might injure yourself. Use the lowest gear possible to keep up with your group (join the fastest division). If you get dropped, it's ok. Try again the next day. Strength is something that requires repeated exercise. It will come in few months. You can't force it's early arrival by doing hill repeats. That's a recipe for disaster.