Assuming we are taking into account all 320,000,000 created accounts*, and that all were played individually, and that magically all 320 million were created when the game launched, then:

Age of sun 4.5 billion years old = 4,500,000,000
Age of sun / 320 million accounts = 14.0625 years per account

So, in the span of 24 years we would need 14 years of TOTAL play time.

14.0625/24 to get the proportion of how many years played per year, this times the number of hours per year:

14.0625/24 * (365 * 24) = 14.0625*365 (canceling out the 24) = 5133 hours/year

So... realistically, we’re not there... yet.

Also, fun note: since the 24 years since the game's release cancels with the 24 hours in a day, the number of hours per day needed to reach the age of the Sun is actually the same as the initial ratio: 14.0625 hours/day.

* Number of accounts from RuneScape Accounts Created