Lol tell that to my dad who is still painting houses at 63. Or his competition who is still painting at 70. that is preposterous. In fact most laborors I know are well above 45. Yeah it takes a toll on your health but most of the health issues I see in labor intensive jobs is because of alcoholism. Its good for your body by and large to get up every day and do physical work. Yes your back will hurt, and your feet and your joints. But you'll be in good health.
Think construction... welders... carpenters... plumbers... guys who smash appendages and crawl around in mud.
I know quite a few old ones and I know many many more who struggle with pain every day as they are my age and talk to me about it. ( IT being my 3rd career after welding and meatcutting ) I have many friends who are dropping out of the workforce and finding alternative jobs because they cant do the work.
Painting is hard work but its one of the less body impacting you can do. There are a few roles like that and yes, being active is a good thing.