Plants are living things, variable in nature. Much like people, they grow at different rates.
If you have rich fertile soil and regular irrigation or rainfall, your plants will grow faster.
If you have poor soil and do not irrigate or feed, or your garden is on a windy or exposed site, your plants may take longer to reach mature size.
If you live in a mild frost-free region, your plants may grow all year round.
If you have very hot summers or very cold winters, your plants may take a break from growing to conserve energy.
Sometimes plants can look like they are not growing, especially when young. That's usually because they prioritise making roots, to support future growth.