Yes. IQ can change over time, but not always for the better. People tend to experience a decline in IQ as they age. The reason is that our brains are not static. They can change and grow throughout our lives. The brain grows through experience, and some of the most crucial learning experiences happen during childhood and adolescence. If you don't get the proper stimulation at these times, your brain will be stunted and unable to progress.
However, other factors also affect your IQ score over time, including stress levels and nutrition. If you were raised in an environment with little exposure to books or languages other than English, this could have affected your ability to learn new things later in life.
Additionally, some studies show that brain size or the amount of white matter in the brain contributes to higher IQ scores later in life; however, this isn't always the case since some people with small brains have high IQs too. So, while it's true that higher IQ scores tend to come with larger brains (and therefore white matter), there are other factors at work here too.