age 40, want to be the grandmaster

how many tactics a day ?

Probably more.

You have a better chance at becoming a brain surgeon . 

I saw her today at the reception

a glass of wine in her hand

I knew she was gonna meet her connection

at her feet was a footloose man

And why "the grandmaster"?  Being "a grandmaster" isn't good enough?

Possibly of interest:

https://www.chess.com/article/view/can-anyone-be-an-im-or-gm

What It Takes to Become a Chess Master by Andrew Soltis

https://web.archive.org/web/20140708093409/http://www.chesscafe.com/text/review857.pdf

Reaching the Top?! by Peter Kurzdorfer

http://www.thechessmind.net/blog/2015/11/16/book-notice-kurzdorfers-reaching-the-top.html

http://www.jeremysilman.com/shop/pc/Reaching-the-Top-77p3905.htm

What It Takes to Become a Grandmaster by GM Andrew Soltis

https://www.chess.com/article/view/don-t-worry-about-your-rating

https://www.chess.com/article/view/am-i-too-old-for-chess

Go for it!!!  

I'm 43 years old, and my goal is to increase my USCF rating to 1 point higher than my previous best. Once I get there, I'll see if I enjoyed the process of getting there enough to shoot for another new best after that.

Becoming a grandmaster isn't about doing tons of tactics. It's about learning about all portions of the game, a little at a time. So shoot for smaller learning and rating goals. As you achieve each one, move on to the next one.

"Every now and then someone advances the idea that one may gain success in chess by using shortcuts. 'Chess is 99% tactics' - proclaims one expert, suggesting that strategic understanding is overrated; 'Improvement in chess is all about opening knowledge' - declares another. A third self-appointed authority asserts that a thorough knowledge of endings is the key to becoming a master; while his expert-friend is puzzled by the mere thought that a player can achieve anything at all without championing pawn structures.

To me, such statements seem futile. You can't hope to gain mastery of any subject by specializing in only parts of it. A complete player must master a complete game ..." - FM Amatzia Avni (2007)

lol

You have an online rating of 750 you are well on your way. 

You have a 50 year advantage over the guy in the other thread who is 92 and wants to be a grandmaster.

You can have more success at becoming a grandfather. And like becoming a grandfather, you should have started over 20 years ago.

Follow your dreams! You'l always regret it if you don't! You can do it! Don't let the nasty negative people here get you down!! They're just jealous of you! Remember, you can do this!! Age means nothing!

Lastly, spend all your life savings on coaches and computers and tournament travel and such.

It's really worth it!

If the OP is that serious, he should study Yusupovs books. It is the most systematic path to chess excellence.

I agree with "El_Oval"

u have much better chances to learn the English!

Do what you like and what you  want, if you want to become a grandmaster, GO FOR IT!!!!

start training now, , read some books and you will come to know what to do and how to do it.

don't waste you brief existence here doing nothing. Don't listen to negative people.

Best of luck sir

All of them