Learn Spanish (Spain): Todavía no me he jubilado, pero pienso mucho en la vejez. - I have not retired yet, but I think a lot about old age.

In Spanish, to say you are thinking 'about' someone or something, you use the combination pensar en. While sobre translates to 'about' in many contexts, it isn't the right preposition to pair with pensar.

Why does this sentence use the reflexive pronoun me with he jubilado?

The verb jubilarse must be reflexive when talking about your own retirement. If you leave out the me, the non-reflexive verb jubilar means to force someone else into retirement or to discard an old object.

Why is the order todavía no instead of the other way around?

In Spanish, you say todavía no (literally 'still not') to express 'not yet.' You can safely place this pair right before the verb. You could also put todavía at the end of the phrase (no me he jubilado todavía), but the no must always stay pinned directly in front of the pronoun me.

I recognise a similarity to viejo, but how is the word vejez formed?

Vejez (old age) is an abstract noun created from the adjective viejo (old). The Spanish suffix -ez is often added to adjectives to create nouns that describe a state or quality, very similar to how we use '-ness' or '-hood' in English.