今日で21歳になりました！って英語でなんて言うの？

Today is my 21st birthday.
I turned 21 today. -This is in the past tense. It means you are no longer 20 years but 21 years today.
*I am 21 years old today.- This is used when someone asks you your age.
For example:
Friend: "How old are you?"
You: "I am 21 years old and today is my birthday."

Turning 21 means you celebrating your birthday in the current year. You can say I am 21 or I will be 21 in April. Depends on how much information you willing to give about yourself.
For example, I am 21 does not say your birthday but that you 21.
I will be 21 in April suggest your birth is in April giving more information.
It is really up to you to decide which you more comfortable with or the situation you dealing with.

First off, Happy Birthday !

I have turned 21 today. = This sentence uses the present perfect tense. The tense is used to show a link between the present and the past in relation to the action. The time of the action is done before now but the result of the action is more important than the action itself.

**you can add years old to be more specific.

I just turned 21 - This means that you became 21 years of age on this day.

Today is my twenty first (21st) birthday. You can also indicate age by saying the number of your birthday.

When explaining to someone how old you are on your birthday either phrases are used equally, So if someone was to say "Happy birthday, How old are you?" you could reply with "Thanks, I am 21 years old today" or "I just turned 21 years old today".

You can use any of these to explain that I just turned 21.

It's my birthday today. I turned 21.

I turned twenty one today.

It is my 21st birthday today.

saying "today is my birthday and i turned 21 years old" lets people know how old you are and that your birthday is today,

"Today I turn 21 years old" and "I'm 21 years old today!"
These expressions are used when it is your birthday and you are turning 21 years old, you can change the number depending on your age, ex. "Today I turn 15 years old" and "I'm 34 years old today!".

If you want explain that you turned 21 today, you can say:
"I turned 21 years old today!"
"Today is my birthday, I turned 21."

To talk about your twenty first birthday is pretty easy in English since people understand what you mean as long as you say "Twenty one!" But in America this is a big deal because that is the legal drinking age and people can stop using fake ID's.

It is easy to explain that you've turned a certain age and there are several ways to express it:

I'm 21 today
Today is my 21st birthday
I turned 21 today

"Today's my birthday! I'm 21 now!", can be used to tell someone how old you are on a specific birthday. First, you can tell the person that today is your birthday. Then you can say your age and the word, "now", to let the person know how old you are in this moment.

"I turned 21 today!", also expresses that today, on your birthday, you turned 21 years old. You could also say, "I turned 21 years old today.", though using the words, "years old", is not necessary.

"I'm 21!", can be used on your birthday or on any other day before your next birthday. It simply lets someone else know the age that you are without referencing which day is your birthday.

Today is my 21st birthday!
MEANING= today's my birthday and you state your age

Today is my birthday, I'm 21 years old!
MEANING= similar to first one

Its my birthday today, I'm 21 today!
MEANING= you can also just say: 'I'm 21 today!'

You can also say:
Happy birthday to me!
Today is 21 years since I was born
Woohoo lets party, its my birthday!
Who fancies some birthday drinks?
*I bought in some cake- its my birthday today!

1. I just turned 21 today.

   2. Today, I am officially 21 years of age.
      これらの両方の声明は、今日が21歳になる私の誕生日であることを意味しています。

   例文は次のようなものです。「一晩中外出して飲みましょう、あなたは今、合法的な成人です」

If you would like to make a joke about becoming 21, you could say:
"This time last year was my twentieth birthday!"
Or, just state that: "Today's my twenty first birthday!" which would be a normal way of saying this.
Alternatively, a very short announcement would suffice:"I'm 21 today!"
However you decide to say it, you should have a happy and enjoyable day.