age 40, want to be the grandmaster

Better chance you'd get a date with Kim Kardashian and it would probably be more fun.
She is deformed and ugly.

I actually think she is ugly too and so are today's professional models imo .
I prefer this, anyway, that's not my wife.

how many tactics a day ?
Try to be good in trolling.
It is sooooooooooooo funny and easier than to become a GM, specially in your 40's.
You can become a GM at age 40 no doubt about it! Don't listen to the negative people here.
I would say 10 hours a day of study chess ( everything not just tactics), 6 days a week, no alcohol and healthy lifestyle( lots of physical exercising), plenty of sleep, 10 years time you CAN become GM.