For a good tax based guide to pensions see-
[broken link removed]
To answer your question-
"The maximum pension contributions, in any one year, for which you are entitled to tax relief, is related to your age and is expressed as a percentage of your gross income. The maximum gross income figure for relief purposes is €262,382 in 2007 and €275,237 in 2008."
NB- age means the age you attain in the particular tax year.
So if you are 29 now and your birthday is in August, for 2008 because you become 30 in 2008 tax year you fall into the 30 to 39 years, i.e. the 20% category, not the under 30, 15% category.