It really does take a long time to get into bicycling shape and, for old timers like us, it takes just that much longer. Just this year I finally got better than terrible at climbing hills. It took practicing all of last year to get there. What I did was find a steep short hill (lots of them around my home) and climb it. Then I'd go back and climb it again and again and again. I trie to accelerate through the whole ordeal as I climbed. When I couldn't do it any more, I'd take a casual bike ride and then head home. Then the next day, I would attack the hill again. Bit by bit I got so I could do the climb more times, faster and with acceleration. I can't tell you how many trips up the hill it took before I gained confidence in my climbing. Hundreds and hundreds of trips to be sure. But in time it got better.
I often ride in the mornings to a little town 7 miles from home. I get coffee and then ride back and it makes a nice morning exercise ride before breakfast. The trip back is uphill. A gentle grade, to be sure, but steadily uphill. I used to pant and struggle at 10mph on that long climb home. This year I've done it at 16 mph and actually enjoyed it. My goal next year is do it in the large chain ring. Somebody before said you have to push yourself. It's true. Take your time. Work at it little by little and you'll get there after enough repetitions.