My "oldest" transaction is from 7/11 (roughly 6 days ago). It has 2983 confirmations, which even at a "slow" estimate of every 10 minutes, that was 8 hours ago. :-S And it doesn't increase when the number of blocks does.
How did you compute that time?
2983 confirmations / 6 confirmations per hour ≐ 497 hours ≐ 21 days.
The result is this big because currently, block are generated much faster than one per 10 minutes.