Is a Pyramid Better?

The answer to your question, should you switch training plans, is yes absolutely. And then in a few weeks switch it again. If all you've been doing is adding weight to the bar week to week, which is a perfectly fine way of doing things, then my guess is that you've stalled not because you're getting older but because your body has adjusted to that program and is no longer making gains. Switching things up will give you renewed gains.

It's not a question of whether one program is better than another - just different. Your way of adding weight to the bar week to week is an excellent way of gaining strength and scores of people have gained strength and muscle this way. It stopped working not because it's a bad program or because you're getting old. The simple fact is that the body cannot gain strength in a linear fashion indefinitely. It would be cool if it could. If we could all add 5 lbs. to our lifts every two weeks, which is a very reasonable progression, that's 10 lbs. a month. Each year, that's a 120 lb. gain. In 8 years, we could all be bench pressing 1,000 lbs. That's just not possible because the body doesn't work that way.