It's best to contribute more earlier than more later, care of the lovely thing that is compound interest- most financial advisers really suck at getting people a secure retirement.
Let's do some simple math for illustration, and say you put in 10% of 100k from the age of 25-45, then increase it to 15% from 45-65. At 45, you have $494,031.52, at 65 you have $3,044,003.59. Now, let's flip it around. At 45 with 15%, you have $741,343.76, and at 65 with 10% you have $3,949,403.04. That's a million dollar difference, and this was all assuming an 8% return throughout, which actually minimizes the difference. If you had an aggressive portfolio at 25-45 that netted 10% followed by a less aggressive portfolio that nets 7.5% from 45-65, the difference grows to $4,712,666.78-$3,373,469.84=$1,339,196.94. That's a lot of money to leave on the table- at a 4% sustainable withdrawal rate, the greater of the two nets you a retirement salary of $188,506.67, while the latter nets you $134,938.79, plus whatever bone social security throws you. And this gives you a good amount of money to leave for your children or grandchildren that would likely be exhausted if you followed the typical financial advice that poor people buy into (spend all your money before you die, save the minimum, leave nothing for your kids, etc).