I always wonder why so many novices will only look at young horses, nothing against you or your friend but imo a horse that has seen everything and knows its job inside out is worth its weight in gold for a novice even if its "past it's prime"
And a good place to look would be a reputable dealer or local papers etc as long as he has someone very knowledgable when viewing any horses. The best way I've found to find a horse is word of mouth maybe try asking around people you know
George is my first horse and I found him on horsemart and only 5 miles from home! I wanted to buy a youngish horse (he was 8 when I got him) as I wanted to buy something for life and although I know there are no guarantees I want to believe and hope that we have many many years ahead of us. Now that may be really novicey and naive but it's how I made my decision!