At what point in life are we motivated by reason more than pleasure?
I don't think they're mutually exclusive or entirely separate concepts. Reason, the following of logic, is useless without pleasure; my computer is 100% reasonable but does nothing of its own volition. Pleasure, a feeling of satisfaction, is reason contrived over millennia of evolution; it's the best way to get an incredibly intelligent species to not kill itself. In a pre-agrarian society, the desire to gorge endlessly drove nomadic humans to hunt and forage, but what was reasonable then leads to overeating now.
We use reason to get what we want, and we want what we do because our ancestors were able to pass on whatever didn't get them killed (unlike their counterparts).
If anything, we're like computers running programs that halt less, but these programs are so bloated and complex that we've mentally divorced them from reason itself, which the OP and its responses show. What pushed a species forward millions of years ago seems nearly incoherent to an individual member today.
Then there's the colloquial definition of "reason" which, similarly, seems to be "pleasure + time." If someone wants to make a lot of money, they could get a job now at a livable wage. If somebody else wants to make a lot of money, they could invest time into eduction, aspiring to later wealth. Both are pursuing their goals reasonably, but the latter requires more time.
Finally, even seemingly unreasonable people tend to pursue pleasure reasonably. Back to overeating: if somebody is hungry and wants to binge, they're more likely to take a reasonable approach (unless they're
@LizKat ) than a dadaist approach (welding a car door to the side of an exposed girder on a dilapidated building sounds
sooo delicious).