Learn Hardcore Portuguese (Portugal): Quando eu era adolescente, não tinha muita disciplina para estudar. - When I was a teenager, I didn’t have much discipline to study.

In quando eu era adolescente, the speaker is describing a general state/period of life (being a teenager), not a single completed event. That’s why the imperfect (era) is used.

If you said quando eu fui adolescente, it would sound odd or wrong to a native speaker, as if “being a teenager” were a short, finished event, like a trip or a party. For ages and long-lasting states in the past, Portuguese almost always uses era.

Why is there no eu before não tinha? Shouldn’t it be eu não tinha?

Portuguese is a “null-subject” language: you can omit subject pronouns when the verb ending already makes it clear who the subject is.

(Eu) tinha = I had
(Ele/Ela) tinha = he/she had

Here, the context quando eu era adolescente already tells us that “I” is the subject, so repeating eu is optional:

Quando eu era adolescente, não tinha muita disciplina para estudar.
= natural and common
Quando eu era adolescente, eu não tinha muita disciplina para estudar.
= also correct, just a bit more emphatic on eu.

Both are grammatically fine; the version without eu before não tinha is very typical in both spoken and written European Portuguese.

Why is tinha used and not tive?

Just like era/fui, tinha/tive is another imperfect vs preterite pair:

tinha – imperfect (a habitual, continuous, or descriptive situation in the past)
tive – preterite (a completed event or a specific occasion)

The sentence is describing a general tendency in that period of life:

não tinha muita disciplina = I generally lacked discipline; that was my usual state.

If you said não tive muita disciplina, it would sound like you’re talking about a specific episode or limited time (e.g. one course, one year, one project), not your overall adolescence. For an ongoing personal characteristic in the past, tinha is the natural choice.

Could the sentence start with Quando era adolescente (dropping eu)?

Yes. In European Portuguese it’s perfectly natural to omit eu here as well:

Quando era adolescente, não tinha muita disciplina para estudar.

The subject “I” is understood from era and tinha. This version is even more typical in informal writing and speech.

So you have three correct options, with slightly different emphasis:

Quando era adolescente, não tinha muita disciplina…
– most neutral, very common
Quando eu era adolescente, não tinha muita disciplina…
– light emphasis on eu at the start
Quando eu era adolescente, eu não tinha muita disciplina…
– stronger emphasis on eu, as in contrast: I didn’t, (maybe others did).

Why is there a comma after Quando eu era adolescente?

In Portuguese, an introductory quando-clause (a time clause at the beginning of the sentence) is normally followed by a comma:

Quando eu era adolescente, não tinha muita disciplina para estudar.

If you put the quando-clause after the main clause, there is usually no comma:

Não tinha muita disciplina para estudar quando eu era adolescente.

Both word orders are correct; what changes is punctuation:

Clause first → comma
Clause after → usually no comma

Why is it muita disciplina and not muito disciplina?

In Portuguese, muito/muita/muitos/muitas must agree in gender and number with the noun it modifies.

disciplina is feminine singular.
Therefore you must use muita (feminine singular).

Examples:

muito dinheiro (masc. sing.)
muita disciplina (fem. sing.)
muitos livros (masc. pl.)
muitas ideias (fem. pl.)

So muito disciplina is incorrect; it breaks gender agreement.

Could I say não tinha muita disciplina nos estudos instead of para estudar?

You could, but the nuance changes slightly:

não tinha muita disciplina para estudar
– focuses on the act of studying: I wasn’t very disciplined about sitting down and studying.
não tinha muita disciplina nos estudos
– focuses more on studies in general (school, academic work), not just the act of studying itself.

Both are valid, but para estudar is very natural and common when you mean self-discipline in the activity of studying.

Why is it para estudar and not a estudar or de estudar?

In this structure, disciplina para + infinitive is the usual pattern:

disciplina para estudar
disciplina para trabalhar
paciência para ouvir

Using para shows purpose or use: discipline for doing something.

Other prepositions would sound unnatural or mean something else here:

disciplina a estudar – incorrect in this sense.
disciplina de estudar – not idiomatic; would sound wrong in European Portuguese.
disciplina em estudar – also strange; not standard usage.

So the natural, idiomatic construction is ter disciplina para + infinitive.

What exactly does disciplina mean here? Is it like a school “subject”?

Disciplina has two main meanings:

Self-discipline / good habits / self-control
– This is the meaning in the sentence: being organized, persistent, able to focus, etc.
School subject / course
– For example, a disciplina de Matemática = the Maths class/subject.

In não tinha muita disciplina para estudar, it clearly means self-discipline, not a school subject. The context (para estudar) makes that clear.

Can não go after the verb, like tinha não muita disciplina?

No. In standard Portuguese, não normally comes directly before the conjugated verb:

não tinha = did not have
não era = was not
não quero = I don’t want

So:

✅ não tinha muita disciplina
❌ tinha não muita disciplina

Putting não after the verb is incorrect in this type of sentence.

Is there any difference between European Portuguese and Brazilian Portuguese in this sentence?

In this specific sentence, there is no real difference between European and Brazilian Portuguese:

Quando eu era adolescente, não tinha muita disciplina para estudar.

It sounds natural in both varieties. Pronunciation will differ, but the grammar and word choice here are shared. Both also allow dropping eu:

Quando era adolescente, não tinha muita disciplina para estudar.

Could I say Quando eu era um adolescente instead of Quando eu era adolescente?

You can grammatically say Quando eu era um adolescente, but in this context, Portuguese usually drops the article and uses the noun like an adjective:

Quando eu era adolescente – most natural and common
Quando eu era um adolescente – correct, but sounds a bit more marked or descriptive, like:
- “When I was a (typical) teenager…” or
- highlighting the category “a teenager” more explicitly.

For talking about your life stage in a neutral way, Quando eu era adolescente is the default.

Can I move para estudar earlier in the sentence, like não tinha para estudar muita disciplina?

No. The natural word order is:

não tinha muita disciplina para estudar

The usual pattern is:

(não) ter + [quantifier] + [noun] + para + [infinitive]

Moving para estudar between tinha and muita disciplina, or between muita and disciplina, would sound wrong:

❌ não tinha para estudar muita disciplina
❌ não tinha muita para estudar disciplina

Keep muita disciplina together, and para estudar after it.