in reality, you don't need all 21 gears, sometime just the one is plenty.
the best thing you can do is to try and stick to one chainring on the front and just change the rear gear instead.
I find people overcompensating themselves by selecting a stupidly spinny gear to start off with and then change gear every second until they're at a reasonable speed to get home on time.
singlespeed is a lovely notion forcing you to not worry about the gearing and just concentrate on riding your bike, what you describe doesn't sound like you're unfit, just that you're not used to riding a bike for a prolong number of miles yet, the more you do it, the easiest it become once your body adapt to riding a bike.
in reality, you don't need all 21 gears, sometime just the one is plenty.
the best thing you can do is to try and stick to one chainring on the front and just change the rear gear instead.
I find people overcompensating themselves by selecting a stupidly spinny gear to start off with and then change gear every second until they're at a reasonable speed to get home on time.
singlespeed is a lovely notion forcing you to not worry about the gearing and just concentrate on riding your bike, what you describe doesn't sound like you're unfit, just that you're not used to riding a bike for a prolong number of miles yet, the more you do it, the easiest it become once your body adapt to riding a bike.