Registering a Trademark

First off, I would like to ask, how old do you have to be (in the US) to register a trademark? I know for a business it is 18 years, but I wasn't sure how different the age limit would be for a trademark. (I've searched for about an hour for this, I even read through several pages on the official government site).

Also, to register one, would I go through a lawyer like you should for a business/LLC, or are there sites online which I can do it and just pay the money through paypal/check/anything else? If I can't get any answers here, my dad should know because I think he's been through this before registering his business (and possibly trademarks too, can't remember).

Thanks for any help,
Andrew