My understanding was that 30+ wasn't a problem, indeed, I got my first aviation job at 30. But the odds are reportedly longer at 35+. The excuse for this ageism is something to do with the brain alegedly slowing at 35.
The fact that both guys I knew who were looking for work at 35+ both found work, the 2 guys on my type rating course who were 35+ (one 40+) being the strongest candidates on the course, and every captain I have flown with saying that low hours guys who are 35+ tend to make better FOs than those aged 21 doesn't seem to count, for some inexplicable reason.
Its possible but undeniaby, however unfair, more difficult.