Lets say you tagged small gun, you started a new char and its 100% right now. Lets say you have 5 int (= 15 sp/lvl)
You gonna max it, so it will take 2x25 to get 125, 3x25 to get 150, 4x25 to get 175, 5x25 to get 200, 6x50 to get 250.
(2x25)+(3x25)+(4x25)+(5x25)+(6x50)=50+75+100+125+300= 650
You would need 650 skill point. But you tagged it, so you get 2% for every single skill point.
650/2 = 325 (this is the real amount of sp you will need for a tag skil)
You get 15 sp per level, you advance 23 level to get lvl24.
15x23 = 345
345>325
So you can max a combat skill even with 5 int, but you will have only 20 skill point remaining for other skills.However if you go with 10 int + education perk, you will have 621 sp total, which means you will have to spend:
325 sp for tagged combat skill to get 250 from 100
175 sp for secondary #1 to get 200 from 100
and remains 121 point for the seondary #2, so you reach 177 from 100.It means later (at level 100 or so) you can max all of your combat skill, max a secondary skill and get all other secondary skill to 177 according to wiki. (
http://fonline-aop.net/wiki/index.php?title=Level_cap)
The maximum skillpoint build is 10 int, educated and the Skilled trait, which lets you 736 sp in total, so you can max everything out (you can do this without education too, which is recommended because you will lose 2 perks due to Skilled trait anyway).
Even with Gifted (you cant tag) + Skilled, you can max a weapon skill, but i dont know what happens to the secondary skills after lvl24 if you tagged none of them (maybe all become unupgradeable)