It would take about 6 months. That's assuming you played every day for 12 hours within that time period. Also assuming you were using that time efficiently.
I maxed in about 2 years . average play time 6 hours a day. did some minigames on the side but mostly went after maxing.
My first year i was on 16 hours a day . got 1700 and Quest point cape within the first month. End of the year (8 months) reached 2000 total. 8 months after that 2200. 7 months after that I maxed. ( I left Runecrafting and Mining last lol )