John,
A lot of good info in this tread. I'll take this conversation in another direction, but a few quick response to everything said here so far. Just for reference I've owned a O'Day 22, (6 years), O'Day 25 (14 years), a Catalina 27 (3 years), and a O'Day 28 (4 years).
1) Welcome to sailing. Great family sport. Wonderful environment, can be relaxed and/or intense, and forever a learning experience.
2) Any 30-40 year old boat is going to need a fair amount of maintenance. Think of the maintenance you would have to do to keep a 1976 Ford Torino as a reliable daily driver!!!! Everything has a weak point. The O'Day 25's is the chainplates. Don't loose sleep over it, just know, it's a weak point that needs to be watched/addressed.
3) Immediately buy this months "Good Old Boat" sail boat magazine. It has an review on O'Day 25's. Great mag.
OK, different direction. Let's enjoy your new purchase. The O'Day 25 is a great boat. I referred to mine as a "small big boat" or a "big small boat". It sails like a boat much bigger than it's size. The deck layout is perfection. Stepping out of the cockpit and onto the deck is comfortable and stable. No awkward motion. Wide side decks on a 25ft, 8ft wide boat (rare)!!! I could be from the cockpit to the bow in seconds, solid and secure the whole way. Moving around that boat was a pleasure, and that cannot be said about many trailerable boats. And your teenagers will spend all their time on the deck, not in the cockpit (boring). How do I know? I had 5 kids, and they spent all of their time on the deck. It is one of the thing they love about sailing (use the whole boat). How important is the deck layout? My family wanted to kill me when I bought the Catalina. The Catalina was not a bad boat, but by comparison the side decks were very narrow and it was difficult to go forward, and the settee were narrow for sleeping.
The O'Day's cabin settees are wide enough to actually sleep on. The cockpit seats are long enough to sleep on. It is a "small big boat". You are going to enjoy your selection.