There have been a lot of discussions about age, you may want to read some other related threads too.
In the not-so-distant past we saw a lot of "career changers" who were older than many of the other applicants, so this is really nothing new. I don't think your age will be an issue in the slightest, particularly with the regionals. They like turnover. The bigger question on the airline's mind will be - "how will you handle flying with a 23-year old who is your captain?"
There have been several posts about the quality of life in today's commercial pilot world and many have extremely valid points. The life of a pilot isn't what it used to be and certainly isn't the coveted position it used to be. I think they're trying to warn you that the grass isn't greener on this side of the fence.
But if flying for an airline is something you truly want to do, then go for it! But I would heed their advice on preparing yourself financially before you make the move. You seem to be in a good paying job (albeit not the best quality of life job) right now - start planning now for the severe pay cut. Scale back your current lifestyle so you'll be ready for $18K /yr and the uncertainty of employment this industry brings. Go in eyes wide open.
Good luck!