Up until a couple of months ago our cat was quite the lap cat, but now he spends most of his time sitting on the grass patch out front, he seems to prefer staying out nearly all the time. Is this normal

Cats are hunters and prowlers, they love to roam, they love to explore.

This is normal. If your cat isn't fixed it could be because he's on the prowl for a mate. If that's the case then it's definitely time to get him fixed, before he finds a female and adds even more kittens into this already overpopulated world.

He's 10yrs old and has been done a long time ago.
He's always been one for laying on your lap & coming /going as he pleases.
The last couple of months he doesn't seem to want to be indoors for any longer than he has to be