Yeah, at least the myocarditis/pericarditis adverse event is limited to the younger age group only. But even this adverse event is very rare, which I doubt would outweigh the risks of potential SARS-CoV-2 infection.

The AstraZeneca's vaccine-associated blood clots, in contrast, seem to have undesirable risk-benefit assessments for younger females in regions with low SARS-CoV-2 infection rates. This is perhaps why some countries have limited the use of this vaccine to the older age group only. But I doubt this is the case for Pfizer's vaccine, at least based on my understanding thus far.