I take too much time to do some things because I overthink and don't looask for help.

Sounds more natural to say "ask for help"

And not just that, my sister gets anger at me because sometimes I forget to give her back the things she haves lent me.

Because your sister gave you those items in the past, we use "has" (past tense) with lend.

However, many people around me say to me that I'm smart.

Sounds a little more natural with removing "to me"

When I ask them why, they tell me that I speak like an older person because of how mature I sound.

The comma helps break up the sentence, it's very long when it's all together

Also, they talk about my grades at university and all the things I do oin a week.

"In" is used when referring to a time period in which an action takes place, like during a week

Other times they just told me that I know many things about many topics, even a friend even called me "enciyclopedia" or "buscador de Google" in a joking way.

Adding "even" here adds emphasis.

I know that intelligence is a lot more complex that it seems, but I don't see myself as a genius.

Also, I think that if you don't have discipline and a striong willpower, intelligence will not be enough to grow and become your best version.

Intelligence

I don't think I'm a smart person.

I suckCOMMENT: In slang, your wording is possible. However, it sounds a bit crass. RECOMMENDED WORDING: I am inept at many things.

FOR SIMPLER: I take too much time to do some things because I often overthink and don't look for helpthings.

And at other times, I have to ask people to repeat what they said to me because I getwas distracted andor didn't hear at all or I just don't get or failed to understand what they awere talking about.

Also, sometimes I'm really clumsy and I have caused a lot of accidents.

GRAMMAR: You can safely delete the 2nd "I."

I have lost many things because of this and broke a lot of glasses.

And not just that, my sister gets angery at me because sometimes I forget to give her back the things she have lent me.

However, many people around me say to me that I'm smart.

OPTION: You can safely delete the word "that."

When I ask them why, they tell memention that I speak like an older person because of how mature I soundwho sounds mature.

Also, they talk about my grades at university and all the things I do on aeach week.

Other times they just told me that I know many things about many topics, even a friend called me "enciyclopedia" or "buscador dea "living Google-bot" in a joking way.

Also, I think that if you don't have discipline and a stringsufficient willpower, intelligence will not be enough to grow and be youractualize the best version of yourself.

I take too much time to do some things because I overthink and don't (look / ask) for help.

I think “ask” is more natural if you mean that you overthink things instead of talking to someone else about it.

And other times, I have to ask people to repeat what they said to me because I geot distracted and didn't hear it at all or I just don't get what they are talking about.

I have this problem too. 😭

I have lost many things because of this and broken a lot of glasses.

And not just that, my sister gets angery at me because sometimes I forget to give her back the things she haves lent me.

However, many people around me say totell me that I'm smart.

Also, they talk about my grades at university and all the things I do on aduring the week.

Other times, they just toldtell me that I know many things about many topics, even adifferent topics. A friend even called me "enciyclopedia" or "buscador de Google" in a joking way.

I know that intelligence is a lot more complex thatn it seems, but I don't see myself as a genius.

Also, I think that if you don't have discipline and a striong willpower, intelligence willis not be enough to grow and be yourcome the best version of yourself.

I have lost many things because of this and broken a lot of glasses.

And not just that, my sister gets angery at me because sometimes I forget to give her back the things she haves lent me.

You could also say "the things she loans me."

However, many people around me say to me that I'm smart.

or "tell me"

When I ask them why, they tell me that I speak like an older person because of how mature I sound.

Also, they talk about my grades at university and all the things I do oin a week.

Other times, they just toldtell me that I know many things about many topics, even a friend called me "enciyclopedia" or "buscador de Google" in a joking way.

I know that intelligence is a lot more complex that it seems, but I don't see myself as a genius.

Also, I think that if you don't have discipline and a striong willpower, intelligence will not be enough to help you grow and be your best version of yourself.

Or "be your best self."

And other times, I have to ask people to repeat what they said to me because I get distracted and didn't hear at all or I just don't get what they are talking about.

I have lost many things because of this and have broken a lot of (eye)glasses.

And not just that, my sister gets angery at me because sometimes I forget to give her back the things sheI have lent meborrowed from her.

I know that intelligence is a lot more complex that it seems, but I don't see myself as a genius.

Also, I think that if you don't have discipline and a striong willpower, intelligence will not be enough to grow and be your best version.