Who is capable of learning and using the strategy? A good third grade math student (are you a good third grade math student?), anyone who can already count cards.
If you can keep a running count addition, subtraction through a deck/s of cards, keeping accurate changing running count, keeping changing memory update through the deck/s.
If you can memorize math flash cards with fast recall or do fast math in your head (division) memorize basic strategy charts, memorize play changes which differentiate from basic strategies.
When should you start practicing the Terrorist Count Strategy? As soon as possible. Third grade students and up who are already interested in Blackjack or will be interested in future years.
How long will it take? Depending on your efforts, goals, desire, determination. Could take less then one year or ten years. It depends on your practice, experience and how fast you learn. If you're serious start as soon as possible!
Should I start practicing Stratking before other counting strategies? YES! Stratking recommends learning and using the Stratking strategy as your first and one and only card counting strategy and use all others only as reference.
Why? You can waste years, a lifetime, all your work, efforts and money down the drain learning and using other count strategies, just to come to realization Stratking is the ticket for all serious players.