Slight sluggishness on crank up

I have a 2012 TRD sport, have had it since last August, it just hit 100k miles and I've been noticing since yesterday a slight delay/sluggishness when I crank it up. I'm the second owner and I don't much on what the previous owner has replaced, does this sound like a starter problem and if so, why isn't any dash icon lighting up, like the check engine? Any help would be much appreciated, thank you.

 

Battery - Check it first.
Your problem sounds like a symptom of a weak battery.
It’s simple enough to check. Most auto parts stores check them for free.

 

Thank you so much for the prompt reply.

 

No, as @TnShooter suggests, more like a battery

Not everything is ECU monitored. The starter being one such item.

 

Oh ok gotcha, thanks as well.