Hello
You haven't actually mentioned if your weight is in proportion to your body or not. For examply, you could be 5ft 4 and 108kg, which would mean that you were quite rotound (hoping that sounds polite enough) but on the other hand, if you was 6ft 2 and 108kg, then that wouldn't be such an issue.
Airlines do have rules on body size for a number of reasons. If you were too small, you wouldn't be able to reach the other head lockers, if you were too tall, you could be bumping the ceiling with your head in turbulence.
Also, at my airline, we have a mixed fleet of aircraft (737 and 319). The 737 has a rather generous sized seat belt on the jump seat but the 319 does not. We had an incident last year where a crew member who was flying as a supernumery on a 319 had to be off-loaded as she couldn't fit in the jump seat, but on a 737 she had no problems
Whilst airlines do like to have pretty crew members, it should all mainly boil down to safety in the end
