I've never come across the 'glass ceiling' so far, and I'm very glad! I've not been practising Aikido long enough to grade yet -in the club where I train there is a compulsory 6-month wait, then sensei decides whether you know your stuff well enough to do the grading. From there, you'll advance if your technique is good enough to pass.
In Jiu Jitsu, which I have been training for 7 years, I have progressed rather more slowly than many people, for various reasons. I'd hate to feel that I was holding someone else back by not grading (or by going for it and failing on account of being not quite ready). Grading progressions should be done according to individual ability, otherwise the whole thing becomes meaningless.