The blood clots from the J&J vaccine have been in women 18 to 48. Lancet reported that the use of birth control pills increases the risk of blood clots by a factor of 3. The vascular effects of the virus itself has been of concern too. Could 2 or 3 of these be interacting to cause blood clots?
Scientists in Europe has suggested as much about the AstraZeneca vaccine which bears some resemblance to the J&J in its employment of viral vector DNA technology as opposed to mRNA technology.
Which is why people under 55 are no longer administered in in countries like France, Canada, England etc...Korea it’s 65?
That being said, clotting in general as it pertains to all ages seems to be a risk inherent even in the rival vaccines.