Get yourself a copy of Airgun World and learn about building safe backstops etc. Then have a look at some of the replica airguns e.g. the K98 replica by, I think Original/Diana. Far better for target practice than an airsoft sniper.
If you want to do targets without running about, try practical pistol airsoft at your own pace.
How about a GSG 1911 and Section 1 license at your local gun club? Some very nice M4, AK, MP40, PPSH and MP5 platforms available.
As Adolf Hamster says, you can always play airsoft at your own pace on a site. If my arthritis plays up I am no racehorse I can tell you!
My best kills today were from hiding until the position was overrun and blatting several players in the back as they advanced passed me. I was sitting down and got myself nice and comfy.