Calculating Employee Leave Accrual

I need some help with leave calculations. The start date is the date they started with the company and this is the base for everything (it is in column "B")

Second criteria is how long they have been with the company I used =(YEAR(NOW())-YEAR(Bxx))*12+MONTH(NOW())-MONTH(Bxx) to determine the months in column H

The employee doesn't earn any leave until after 6 months. On the 6th month anniversary they automatically receive 12 days (96hrs) and an additional 2 days (16 Hrs) each month thereafter. Now if that were the end it would be simple with =IF(Hxx<6,0,Hxx*2) in column I. However, once at the employee reaches 12 months they are awarded 30 days with the maximum accumulation being 60 days.

So if written out it would look like this:
1-5 months = 0 days of leave
6-12 months = 12 days plus 2 days per month (total for the first year 24 days)
12 months and more = 30 days a year not to exceed 60 days.
Note: The leave days do not accumulate when advancing in time. Example: if the employee uses 6 days during his 10th month with the company when he gets to one year he will have 24 days available.

Once I get this, any leave taken can simply be subtracted from this total.

Any questions let me know, thanks in advance for any assistance.

Kyle