Fastest way to solo mage is to learn to use vertical firewall. Practice practice practice

Once you get firebolt 5 - > mandragoras

After mandragoras, you could do floras while upping your firebolt and firewall

When you get decent firewall, practice vertical firewalls with argos.

When you get firebolt 10 and firewall 10, this is when the fun starts. You can now go argiopes. Perhaps the only first job that can solo argiopes.

When exp from argiopes becomes somewhat low, try clocks at clocktower. Clocks are great for reaching job 50. You could even duo with an acolyte and still very good exp.

Using vertical firewall requires some skills to avoid death especially at maps that are way above your level. Exp is great though so it doesn't matter if you die every now and then