Here are some good tips for germinating seeds that are hard to start or are having trouble germinating. Have some patience though as it could take anywhere from three days to three weeks for a seed to germinate. Some of these tricks I would only use if the seed has not sprouted after two to three weeks or if you have a few seeds in reserve from a batch that haven't germinated. 

Seeds are comprised of an outer hard layer and an embryo which is inside the hard shell. The reason that older seeds don't germinatem well is that the shell has become to hard and water is unable to penetrate, this process of imbibition is the start of the germination process. The seed will swell with water and eventually the shell will pop open and a small tap root will erupt. 

One thing i wouldn't do is to germinate your seeds on a paper towel. White paper is filled with bleach and other chemicals and is not a good thing for your plants. Use small jiffy starter blocks or a light soil:

1. Dilute 10ml (roughly one tsp) of Fulvic acid per litre (33 oz) of water. 

2. Scuff the outer shell of the seed with some sand paper. Roll up a small cigar or sand paper or line a match box and gently shake the seeds over it. This will create micro abrasions letting in more water.

3. Use a lightly carbonated water. The extra Co2 will help the water penetrate the seed.

4. Use a light enzyme or seed booster, Plagron Nutrients has a very good one. 

5. Finally if all else fails use an Exacto knife to slightly slice the seed open down the spine of the seed. This will make it easier for water to penetrate the shell.