It is possible (although somewhat unlikely) that you had absolutely no
astigmatism when younger and developed it later in your life, but just
because you need glasses when you get older does not mean that the shape of
your eyes has changed. When you are younger your eye muscles are better able
to bend the lens in your eye to correct for these problems and focus
correctly. As you get older, the lens in your eye gets stiffer, and your eye
muscles may get weaker may it harder to compensate for these irregularities
in the shape of your eye.

As you get older, you are also likely to need to reading glasses (for same
reasons as stated above about getting older), or progressives if you want to
see clearly at far and near distances at the same time. With your vision,
you could probably get by with just reading glasses unless the astigmatism
correction at a distance is important to you.

Also, a cylinder correction of -1.50 is not equivalent in power to a sphere
correction of 1.50. The actual effect is about half, but the details of this
are beyond my technical expertise. I wouldn't worry about it if I were you.
But discuss it with your OD if you are concerned.