Yes, you can go for 2019 intake as there is no such eligibility criteria in GRE. You can register for the test irrespective of age.

However, you have to fulfil the GRE eligibility criteria for individual institutes where you are applying.

The are four sections in GRE General test- Verbal Reasoning, Quantitative Reasoning and Analytical Writing. There are seven GRE subject tests:

• Biochemistry, Cell and Molecular Biology
• Biology
• Chemistry
• Literature in English
• Mathematics
• Physics
• Psychology

To have more inforamtion you can refer below link

GRE Eligibility Criteria

Yes, you can apply for spring 2019 intake as you are eligible beacuse GRE score is valid for 5 years. So plan and prepare accordingly to get admission in your desired college/country. Along with this, you will have to give English proficiency test  (TOEFL) also.

Good Luck!!!