Dee,
Drainpipes, trellises, pagodas, flat roofed extensions make climbing upto an upstairs window quite feasible for most people, virtually easy for anyone with the proper motivation.
Large scale masonry or stone built houses with depressed pointing would be difficult but doable at a push.
Climbing a standard brick wall, with not much else for help would be strictly for experts only.
This of course is just my opinion, but in a previous life (where I was thirty pounds lighter), I used to be a rock climber, so I think I’m probably close to the truth.
Hope it helps.
Cheers, Grinder
)