My brother is the perfect example. He has lifted for a couple of years and, in that time, he has deadlifted 415 pounds and benched 225 pounds. Impressive numbers? In the powerlifting world, no. Better than the average dude going to the rec center? Sure. With those lifts, some "experts" might go as far as to say he is an "intermediate" lifter.
As an "intermediate" lifter, progress is supposed to be slower. You should not be able to add weight to the bar each and every session. Or, at least that is what the "experts" say. Well, as an "intermediate" lifter, my brother added 100 pounds to his five rep squat in just about 3 months. He squatted three times a week, doing three sets of five across, and he usually added five pounds to the bar every session. He started his progression with a relatively easy 215 pounds for three sets of five, and he ended it with 315 pounds for three sets of five.
Sure, his squat had a lot of room for improvement when he started his progression. But, a lot of "experts" would have said that progress like that is not possible unless you just started lifting. They say only "newbies" can follow linear progressions, and, after six months to a year of lifting, you have to get all fancy to get stronger.
Well, here is a guy who has been lifting for about two and a half years, and he made progress like he was just starting out:
The take home message: Experience level is not about how long you have been lifting, it is about the amount of weight you can lift. If you have been lifting for a few years and you have a lift that is lagging behind, then keep things simple and grind out a basic linear progression. You're not as advanced as you think. In fact, if you cannot squat 300 pounds as an adult male, you are probably still a beginner.
Just some food for thought.