Metaphysics is, per Merriam-Webster,
a (1) : a division of philosophy that is concerned with the fundamental nature of reality and being and that includes ontology, cosmology, and often epistemology
(2) : ontology 2
b : abstract philosophical studies : a study of what is outside objective experience
which I think may be what you are trying to get at in your description of "thinking philosophically about life". If so, you can use the verb metaphysicize:
: to engage in metaphysical speculation
You wouldn't even need to use the last two words of your sentence; you could simply say
Here we stand, around ten or fifteen years ago, when I started metaphysicizing/to metaphysicize.
You don't need to say "about life" since the word on its own includes thinking philosophically about life, the universe, and everything.
On the other hand, if you don't so much mean that you started thinking deep thoughts about life but rather that you became more philosophical about life, in the sense
2 : characterized by the attitude of a philosopher; specifically : calm or unflinching in the face of trouble, defeat, or loss
then you may want to use a longer phrase like "to become more philosophical" or "to be more contemplative" or "to attain serenity".