I don't think this horse looks that bad, certainly not muley. They just aren't the most flattering photos. He's a little easy in the topline due to age. Realistically, no one knows how long a 24 year old horse will be ride-able. It depends on how hard the miles have been and how well he was cared for, as well as what sort of ageing runs in his family, injuries he's sustained, etc. His legs are pretty doggone clean for all the age he's got on him. He doesn't even have any filling in his legs or any 'jewelry' on them. No curbs, no obvious signs of anything.
Occasionally I run into a 'low mileage' oldster who simply hasn't gotten any hard miles put on him, and these horses can be completely comfortable working lightly for quite some time. In fact, a little reasonable exercise keeps these fellows limber and comfortable.
If the OP were to be determined to gallop and jump, or show every weekend in ten classes, or cut, or rein, I think the choice of the horse would be a very finely divided matter and I'd be dissecting his conformation. But if I recall, she's interested in riding casually, lightly, at slower gaits.
And an older horse can be ideal for that. It might be a good match, as long as you understand that no one can say how long a 24 year old will be working. It really depends on what really - realistically - you'll be doing - riding hard or light.
My friend has a 35 year old she rides lightly, and enjoys. He also 'babysits' her younger horse. Another gal I know had a horse she raised and rode lightly - the horse was still being ridden at 30, but of course, lightly. Another gal I know bought a 20 year old school horse. He's thriving under her care. He's taken better care of than the Olympic winners, LOL. She really is not at all interested in riding intensely - she walks mostly, and trots a little in the ring, and then they just enjoy each other's company. She doesn't want to get pushed to do more, so she and the horse are perfect for each other.
Sometimes this is the best thing - for a person to regain their confidence on a trusted old friend, and to give that trusted friend a good home where he can be comfortable and well-treated.