As a person fortunate to be studying philosophy and by this i meaning having the time to sit and think for large quantities of time without the worries that everyday life can give I have pondered a great deal the meaning of rationality, reasoned judgement and decision making.
I believe that it is entirely reasonable for someone to choose to commit suicide on rational grounds if rational is that which can be put into a valid logical form that is backed up by intuitively sound premises. Disability is something of a relative term built in a societal construct. Is needing glasses a disability? in the same way as missing limbs?
Is it irrational to choose to commit suicide on the basis that you want to experience it and simply cannot wait such and such years. I wouldn't say we know for sure what death is, none of us has experienced it directly and those that have don't tend to speak about it. For many people Death is oncoming doom filled with anxiety and fear and often we deal with the same feelings by facing them head on as opposed to ignoring or running away. An example of a thing that may produce the same feelings could be; an important exam, starting a new job, doing anything new really.
Anyway, that's my opinion and thanks for listening
Ry