Hi fella and welcome to the big boys playground.?
As already said you will love it and airsofters are generally a very friendly bunch willing and eager to impart their knowledge and expertise for free.
Nobody will care about how you look,what kit you have or your ability to run a 100yd dash in 10 seconds or take out a whole team before lunch.
Get yourself out there and you will soon overcome any shyness and nerves ?
Take things at a pace that you find comfortable and after a while I'm sure your fitness levels will improve.
I'm no spring chicken and not gonna break any records for agility (I could,however,break hundreds if i sat on them lol) but I pay my money and that means I play as I want to and that way I get more enjoyment without any pressure.
Play and have fun??
Regards
Ps.I like a beer as well ?