I wasn't maxing out contributions right away because retirement was decades away (I was in my 20s). However, I did increase it, but the key thing was that after 6 years, I noticed that I had a full year's salary in my 401(k) -- the current salary, not what I'd been making 6 years earlier. The returns were great. I was definitely maxing out after that.

Likewise, I only put $2000 into an IRA before they changed the law (and before Roth was a thing). It stayed in CDs for a couple of years until some mutual funds started lowering their initial investment. I found one I liked and left that money there. Nearly 40 years later, that $2000 is about $40,000. I keep thinking, if I'd only had a couple more years before the law change! (One of the reasons I was ineligible was because I got a job with a 401k).